* [PATCH v21 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
The clone_args structure is extensible, with the syscall passing in the
length of the structure. Inside the kernel we use copy_struct_from_user()
to read the struct but this has the unfortunate side effect of silently
accepting some overrun in the structure size providing the extra data is
all zeros. This means that we can't discover the clone3() features that
the running kernel supports by simply probing with various struct sizes.
We need to check this for the benefit of test systems which run newer
kselftests on old kernels.
Add a flag which can be set on a test to indicate that clone3() may return
-E2BIG due to the use of newer struct versions. Currently no tests need
this but it will become an issue for testing clone3() support for shadow
stacks, the support for shadow stacks is already present on x86.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e066b201fa64..5b8b7d640e70 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -39,6 +39,7 @@ struct test {
size_t size;
size_function size_function;
int expected;
+ bool e2big_valid;
enum test_mode test_mode;
filter_function filter;
};
@@ -146,6 +147,11 @@ static void test_clone3(const struct test *test)
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
getpid(), ret, test->expected);
if (ret != test->expected) {
+ if (test->e2big_valid && ret == -E2BIG) {
+ ksft_print_msg("Test reported -E2BIG\n");
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
getpid(), ret, test->expected);
--
2.47.2
^ permalink raw reply related
* [PATCH v21 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-09-15 23:12 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Shuah Khan
In-Reply-To: <20250916-clone3-shadow-stack-v21-0-910493527013@kernel.org>
Add basic test coverage for specifying the shadow stack for a newly
created thread via clone3(), including coverage of the newly extended
argument structure. We check that a user specified shadow stack can be
provided, and that invalid combinations of parameters are rejected.
In order to facilitate testing on systems without userspace shadow stack
support we manually enable shadow stacks on startup, this is architecture
specific due to the use of an arch_prctl() on x86. Due to interactions with
potential userspace locking of features we actually detect support for
shadow stacks on the running system by attempting to allocate a shadow
stack page during initialisation using map_shadow_stack(), warning if this
succeeds when the enable failed.
In order to allow testing of user configured shadow stacks on
architectures with that feature we need to ensure that we do not return
from the function where the clone3() syscall is called in the child
process, doing so would trigger a shadow stack underflow. To do this we
use inline assembly rather than the standard syscall wrapper to call
clone3(). In order to avoid surprises we also use a syscall rather than
the libc exit() function., this should be overly cautious.
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 143 +++++++++++++++++++++-
tools/testing/selftests/clone3/clone3_selftests.h | 63 ++++++++++
2 files changed, 205 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index 5b8b7d640e70..05c3d2dcbf2a 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -3,6 +3,7 @@
/* Based on Christian Brauner's clone3() example */
#define _GNU_SOURCE
+#include <asm/mman.h>
#include <errno.h>
#include <inttypes.h>
#include <linux/types.h>
@@ -11,6 +12,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
+#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/un.h>
@@ -19,8 +21,12 @@
#include <sched.h>
#include "../kselftest.h"
+#include "../ksft_shstk.h"
#include "clone3_selftests.h"
+static bool shadow_stack_supported;
+static size_t max_supported_args_size;
+
enum test_mode {
CLONE3_ARGS_NO_TEST,
CLONE3_ARGS_ALL_0,
@@ -28,6 +34,10 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+ CLONE3_ARGS_SHADOW_STACK,
+ CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
};
typedef bool (*filter_function)(void);
@@ -44,6 +54,44 @@ struct test {
filter_function filter;
};
+
+/*
+ * We check for shadow stack support by attempting to use
+ * map_shadow_stack() since features may have been locked by the
+ * dynamic linker resulting in spurious errors when we attempt to
+ * enable on startup. We warn if the enable failed.
+ */
+static void test_shadow_stack_supported(void)
+{
+ long ret;
+
+ ret = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
+ if (ret == -1) {
+ ksft_print_msg("map_shadow_stack() not supported\n");
+ } else if ((void *)ret == MAP_FAILED) {
+ ksft_print_msg("Failed to map shadow stack\n");
+ } else {
+ ksft_print_msg("Shadow stack supportd\n");
+ shadow_stack_supported = true;
+
+ if (!shadow_stack_enabled)
+ ksft_print_msg("Mapped but did not enable shadow stack\n");
+ }
+}
+
+static void *get_shadow_stack_page(unsigned long flags)
+{
+ unsigned long long page;
+
+ page = syscall(__NR_map_shadow_stack, 0, getpagesize(), flags);
+ if ((void *)page == MAP_FAILED) {
+ ksft_print_msg("map_shadow_stack() failed: %d\n", errno);
+ return 0;
+ }
+
+ return (void *)page;
+}
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -57,6 +105,7 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
} args_ext;
pid_t pid = -1;
+ void *p;
int status;
memset(&args_ext, 0, sizeof(args_ext));
@@ -89,6 +138,26 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
args.exit_signal = 0x00000000000000f0ULL;
break;
+ case CLONE3_ARGS_SHADOW_STACK:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_MISALIGNED:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *) - 1;
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NO_TOKEN:
+ p = get_shadow_stack_page(0);
+ p += getpagesize() - sizeof(void *);
+ args.shstk_token = (unsigned long long)p;
+ break;
}
memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -102,7 +171,12 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
if (pid == 0) {
ksft_print_msg("I am the child, my PID is %d\n", getpid());
- _exit(EXIT_SUCCESS);
+ /*
+ * Use a raw syscall to ensure we don't get issues
+ * with manually specified shadow stack and exit handlers.
+ */
+ syscall(__NR_exit, EXIT_SUCCESS);
+ ksft_print_msg("CHILD FAILED TO EXIT PID is %d\n", getpid());
}
ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
@@ -184,6 +258,26 @@ static bool no_timenamespace(void)
return true;
}
+static bool have_shadow_stack(void)
+{
+ if (shadow_stack_supported) {
+ ksft_print_msg("Shadow stack supported\n");
+ return true;
+ }
+
+ return false;
+}
+
+static bool no_shadow_stack(void)
+{
+ if (!shadow_stack_supported) {
+ ksft_print_msg("Shadow stack not supported\n");
+ return true;
+ }
+
+ return false;
+}
+
static size_t page_size_plus_8(void)
{
return getpagesize() + 8;
@@ -327,6 +421,50 @@ static const struct test tests[] = {
.expected = -EINVAL,
.test_mode = CLONE3_ARGS_NO_TEST,
},
+ {
+ .name = "Shadow stack on system with shadow stack",
+ .size = 0,
+ .expected = 0,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with misaligned address",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with normal memory",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with no token",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack on system without shadow stack",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = have_shadow_stack,
+ },
};
int main(int argc, char *argv[])
@@ -334,9 +472,12 @@ int main(int argc, char *argv[])
size_t size;
int i;
+ enable_shadow_stack();
+
ksft_print_header();
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
+ test_shadow_stack_supported();
for (i = 0; i < ARRAY_SIZE(tests); i++)
test_clone3(&tests[i]);
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index 939b26c86d42..147b4ed36b5c 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -31,12 +31,75 @@ struct __clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+#ifndef CLONE_ARGS_SIZE_VER2
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#endif
+ __aligned_u64 shstk_token;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
+#endif
};
+/*
+ * For architectures with shadow stack support we need to be
+ * absolutely sure that the clone3() syscall will be inline and not a
+ * function call so we open code.
+ */
+#ifdef __x86_64__
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("rax") = __NR_clone3;
+ register long _args __asm__ ("rdi") = (long)(args);
+ register long _size __asm__ ("rsi") = (long)(size);
+ long ret;
+
+ __asm__ volatile (
+ "syscall\n"
+ : "=a"(ret)
+ : "r"(_args), "r"(_size),
+ "0"(_num)
+ : "rcx", "r11", "memory", "cc"
+ );
+
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+
+ return ret;
+}
+#elif defined(__aarch64__)
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("x8") = __NR_clone3;
+ register long _args __asm__ ("x0") = (long)(args);
+ register long _size __asm__ ("x1") = (long)(size);
+ register long arg2 __asm__ ("x2") = 0;
+ register long arg3 __asm__ ("x3") = 0;
+ register long arg4 __asm__ ("x4") = 0;
+
+ __asm__ volatile (
+ "svc #0\n"
+ : "=r"(_args)
+ : "r"(_args), "r"(_size),
+ "r"(_num), "r"(arg2),
+ "r"(arg3), "r"(arg4)
+ : "memory", "cc"
+ );
+
+ if ((int)_args < 0) {
+ errno = -((int)_args);
+ return -1;
+ }
+
+ return _args;
+}
+#else
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
return syscall(__NR_clone3, args, size);
}
+#endif
static inline void test_clone3_supported(void)
{
--
2.47.2
^ permalink raw reply related
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Askar Safin @ 2025-09-16 1:04 UTC (permalink / raw)
To: Christian Brauner
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Al Viro, Jan Kara, Christoph Hellwig, Jens Axboe, Andy Shevchenko,
Aleksa Sarai, Thomas Weißschuh, Julian Stecklina, Gao Xiang,
Art Nikpal, Andrew Morton, Alexander Graf, Rob Landley,
Lennart Poettering, linux-arch, linux-alpha, linux-snps-arc,
linux-arm-kernel, linux-csky, linux-hexagon, loongarch,
linux-m68k, linux-mips, linux-openrisc, linux-parisc,
linuxppc-dev, linux-riscv, linux-s390, linux-sh, sparclinux,
linux-um, x86, Ingo Molnar, linux-block, initramfs, linux-api,
linux-doc, linux-efi, linux-ext4, Theodore Y . Ts'o,
linux-acpi, Michal Simek, devicetree, Luis Chamberlain, Kees Cook,
Thorsten Blum, Heiko Carstens, patches
In-Reply-To: <20250915-modebranche-marken-fc832a25e05d@brauner>
On Mon, Sep 15, 2025 at 4:34 PM Christian Brauner <brauner@kernel.org> wrote:
> Split it up into multiple patch series. Send a first series that
> focusses only on removing the generic infrastructure keeping it as
> contained as possible. Only do non-generic cleanups that are absolutely
> essential for the removal. Then the cleanups can go in separate series
> later.
Ok, I will do this.
I will send a minimal patchset with arch/ changes kept to absolute minimum
or even absent. Nearly all of the changes will be in init/ and docs.
Hopefully it will pass via the VFS tree.
If it gets to kernel release, I will consider sending more patchsets.
--
Askar Safin
^ permalink raw reply
* Re: [PATCH 00/62] initrd: remove classic initrd support
From: Dave Young @ 2025-09-16 1:48 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250912223937.3735076-1-safinaskar@zohomail.com>
Hi,
On Sat, 13 Sept 2025 at 06:42, Askar Safin <safinaskar@zohomail.com> wrote:
>
> Intro
> ====
> This patchset removes classic initrd (initial RAM disk) support,
> which was deprecated in 2020.
> Initramfs still stays, and RAM disk itself (brd) still stays, too.
There is one initrd use case in my mind, it can be extended to co-work
with overlayfs as a kernel built-in solution for initrd(compressed fs
image)+overlayfs. Currently we can use compressed fs images
(squashfs or erofs) within initramfs, and kernel loop mount together
with overlayfs, this works fine but extra pre-mount phase is needed.
Thanks
Dave
^ permalink raw reply
* Re: [PATCH RESEND 28/62] init: alpha, arc, arm, arm64, csky, m68k, microblaze, mips, nios2, openrisc, parisc, powerpc, s390, sh, sparc, um, x86, xtensa: rename initrd_{start,end} to virt_external_initramfs_{start,end}
From: Rob Herring @ 2025-09-16 3:09 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250913003842.41944-29-safinaskar@gmail.com>
On Sat, Sep 13, 2025 at 12:38:07AM +0000, Askar Safin wrote:
> Rename initrd_start to virt_external_initramfs_start and
> initrd_end to virt_external_initramfs_end.
There's not really any point in listing every arch in the subject.
Rob
^ permalink raw reply
* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Yury Khrustalev @ 2025-09-16 12:29 UTC (permalink / raw)
To: Mark Brown
Cc: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan,
linux-kernel, Catalin Marinas, Will Deacon, jannh, Andrew Morton,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-4-910493527013@kernel.org>
On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the shadow
> stack for a new thread, instead the kernel will dynamically allocate a
> new shadow stack with the same size as the normal stack. This appears to
> be due to the shadow stack series having been in development since
> before the more extensible clone3() was added rather than anything more
> deliberate.
>
> Add a parameter to clone3() specifying a shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active. If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
>
> ...
>
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
>
> Portions of the x86 architecture code were written by Rick Edgecombe.
>
> Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
I've tested this version together with my Glibc patches [1]. No issues
to report.
Tested-by: Yury Khrustalev <yury.khrustalev@arm.com>
[1]: https://inbox.sourceware.org/libc-alpha/20250916122757.2341920-1-yury.khrustalev@arm.com/
> ---
> arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
> arch/x86/include/asm/shstk.h | 11 +++--
> arch/x86/kernel/process.c | 2 +-
> arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
> include/asm-generic/cacheflush.h | 11 +++++
> include/linux/sched/task.h | 17 ++++++++
> include/uapi/linux/sched.h | 9 ++--
> kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
> 8 files changed, 217 insertions(+), 26 deletions(-)
>
> diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
> index 3abcbf9adb5c..fd1d5a6655de 100644
> --- a/arch/arm64/mm/gcs.c
> +++ b/arch/arm64/mm/gcs.c
> @@ -43,8 +43,23 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
> {
> unsigned long addr, size;
>
> - if (!system_supports_gcs())
> + if (!system_supports_gcs()) {
> + if (args->shstk_token)
> + return -EINVAL;
> +
> return 0;
> + }
> +
> + /*
> + * If the user specified a GCS then use it, otherwise fall
> + * back to a default allocation strategy. Validation is done
> + * in arch_shstk_validate_clone().
> + */
> + if (args->shstk_token) {
> + tsk->thread.gcs_base = 0;
> + tsk->thread.gcs_size = 0;
> + return 0;
> + }
>
> if (!task_gcs_el0_enabled(tsk))
> return 0;
> @@ -68,6 +83,36 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
> return 0;
> }
>
> +static bool gcs_consume_token(struct vm_area_struct *vma, struct page *page,
> + unsigned long user_addr)
> +{
> + u64 expected = GCS_CAP(user_addr);
> + u64 *token = page_address(page) + offset_in_page(user_addr);
> +
> + if (!cmpxchg_to_user_page(vma, page, user_addr, token, expected, 0))
> + return false;
> + set_page_dirty_lock(page);
> +
> + return true;
> +}
> +
> +int arch_shstk_validate_clone(struct task_struct *tsk,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + unsigned long gcspr_el0;
> + int ret = 0;
> +
> + gcspr_el0 = args->shstk_token;
> + if (!gcs_consume_token(vma, page, gcspr_el0))
> + return -EINVAL;
> +
> + tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
> +
> + return ret;
> +}
> +
> SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
> {
> unsigned long alloc_size;
> diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
> index 0f50e0125943..827e983430aa 100644
> --- a/arch/x86/include/asm/shstk.h
> +++ b/arch/x86/include/asm/shstk.h
> @@ -6,6 +6,7 @@
> #include <linux/types.h>
>
> struct task_struct;
> +struct kernel_clone_args;
> struct ksignal;
>
> #ifdef CONFIG_X86_USER_SHADOW_STACK
> @@ -16,8 +17,8 @@ struct thread_shstk {
>
> long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
> void reset_thread_features(void);
> -unsigned long shstk_alloc_thread_stack(struct task_struct *p, u64 clone_flags,
> - unsigned long stack_size);
> +unsigned long shstk_alloc_thread_stack(struct task_struct *p,
> + const struct kernel_clone_args *args);
> void shstk_free(struct task_struct *p);
> int setup_signal_shadow_stack(struct ksignal *ksig);
> int restore_signal_shadow_stack(void);
> @@ -28,8 +29,10 @@ static inline long shstk_prctl(struct task_struct *task, int option,
> unsigned long arg2) { return -EINVAL; }
> static inline void reset_thread_features(void) {}
> static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p,
> - u64 clone_flags,
> - unsigned long stack_size) { return 0; }
> + const struct kernel_clone_args *args)
> +{
> + return 0;
> +}
> static inline void shstk_free(struct task_struct *p) {}
> static inline int setup_signal_shadow_stack(struct ksignal *ksig) { return 0; }
> static inline int restore_signal_shadow_stack(void) { return 0; }
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index e3a3987b0c4f..e8c8447cc0fd 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -209,7 +209,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> * is disabled, new_ssp will remain 0, and fpu_clone() will know not to
> * update it.
> */
> - new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size);
> + new_ssp = shstk_alloc_thread_stack(p, args);
> if (IS_ERR_VALUE(new_ssp))
> return PTR_ERR((void *)new_ssp);
>
> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
> index 5eba6c5a6775..56893523b6f2 100644
> --- a/arch/x86/kernel/shstk.c
> +++ b/arch/x86/kernel/shstk.c
> @@ -191,18 +191,61 @@ void reset_thread_features(void)
> current->thread.features_locked = 0;
> }
>
> -unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
> - unsigned long stack_size)
> +int arch_shstk_validate_clone(struct task_struct *t,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + void *maddr = page_address(page);
> + unsigned long token;
> + int offset;
> + u64 expected;
> +
> + /*
> + * kernel_clone_args() verification assures token address is 8
> + * byte aligned.
> + */
> + token = args->shstk_token;
> + expected = (token + SS_FRAME_SIZE) | BIT(0);
> + offset = offset_in_page(token);
> +
> + if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
> + expected, 0))
> + return -EINVAL;
> + set_page_dirty_lock(page);
> +
> + return 0;
> +}
> +
> +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
> + const struct kernel_clone_args *args)
> {
> struct thread_shstk *shstk = &tsk->thread.shstk;
> + u64 clone_flags = args->flags;
> unsigned long addr, size;
>
> /*
> * If shadow stack is not enabled on the new thread, skip any
> - * switch to a new shadow stack.
> + * implicit switch to a new shadow stack and reject attempts to
> + * explicitly specify one.
> */
> - if (!features_enabled(ARCH_SHSTK_SHSTK))
> + if (!features_enabled(ARCH_SHSTK_SHSTK)) {
> + if (args->shstk_token)
> + return (unsigned long)ERR_PTR(-EINVAL);
> +
> return 0;
> + }
> +
> + /*
> + * If the user specified a shadow stack then use it, otherwise
> + * fall back to a default allocation strategy. Validation is
> + * done in arch_shstk_validate_clone().
> + */
> + if (args->shstk_token) {
> + shstk->base = 0;
> + shstk->size = 0;
> + return args->shstk_token + 8;
> + }
>
> /*
> * For CLONE_VFORK the child will share the parents shadow stack.
> @@ -222,7 +265,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, u64 clone_flags,
> if (!(clone_flags & CLONE_VM))
> return 0;
>
> - size = adjust_shstk_size(stack_size);
> + size = adjust_shstk_size(args->stack_size);
> addr = alloc_shstk(0, size, 0, false);
> if (IS_ERR_VALUE(addr))
> return addr;
> diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
> index 7ee8a179d103..96cc0c7a5c90 100644
> --- a/include/asm-generic/cacheflush.h
> +++ b/include/asm-generic/cacheflush.h
> @@ -124,4 +124,15 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
> } while (0)
> #endif
>
> +#ifndef cmpxchg_to_user_page
> +#define cmpxchg_to_user_page(vma, page, vaddr, ptr, old, new) \
> +({ \
> + bool ret; \
> + \
> + ret = try_cmpxchg(ptr, &old, new); \
> + flush_icache_user_page(vma, page, vaddr, sizeof(*ptr)); \
> + ret; \
> +})
> +#endif
> +
> #endif /* _ASM_GENERIC_CACHEFLUSH_H */
> diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
> index 34d6a0e108c3..96fb485ff2dd 100644
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -16,6 +16,7 @@ struct task_struct;
> struct rusage;
> union thread_union;
> struct css_set;
> +struct vm_area_struct;
>
> /* All the bits taken by the old clone syscall. */
> #define CLONE_LEGACY_FLAGS 0xffffffffULL
> @@ -44,6 +45,7 @@ struct kernel_clone_args {
> struct cgroup *cgrp;
> struct css_set *cset;
> unsigned int kill_seq;
> + unsigned long shstk_token;
> };
>
> /*
> @@ -226,4 +228,19 @@ static inline void task_unlock(struct task_struct *p)
>
> DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
>
> +#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
> +int arch_shstk_validate_clone(struct task_struct *p,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args);
> +#else
> +static inline int arch_shstk_validate_clone(struct task_struct *p,
> + struct vm_area_struct *vma,
> + struct page *page,
> + struct kernel_clone_args *args)
> +{
> + return 0;
> +}
> +#endif
> +
> #endif /* _LINUX_SCHED_TASK_H */
> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> index 359a14cc76a4..7e18e7b3df3a 100644
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -84,6 +84,7 @@
> * kernel's limit of nested PID namespaces.
> * @cgroup: If CLONE_INTO_CGROUP is specified set this to
> * a file descriptor for the cgroup.
> + * @shstk_token: Pointer to shadow stack token at top of stack.
> *
> * The structure is versioned by size and thus extensible.
> * New struct members must go at the end of the struct and
> @@ -101,12 +102,14 @@ struct clone_args {
> __aligned_u64 set_tid;
> __aligned_u64 set_tid_size;
> __aligned_u64 cgroup;
> + __aligned_u64 shstk_token;
> };
> #endif
>
> -#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> -#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
> -#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> +#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
> +#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
>
> /*
> * Scheduling policies
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d6e1fb11eff9..0dbfc8828e08 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1907,6 +1907,51 @@ static bool need_futex_hash_allocate_default(u64 clone_flags)
> return true;
> }
>
> +static int shstk_validate_clone(struct task_struct *p,
> + struct kernel_clone_args *args)
> +{
> + struct mm_struct *mm;
> + struct vm_area_struct *vma;
> + struct page *page;
> + unsigned long addr;
> + int ret;
> +
> + if (!IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK))
> + return 0;
> +
> + if (!args->shstk_token)
> + return 0;
> +
> + mm = get_task_mm(p);
> + if (!mm)
> + return -EFAULT;
> +
> + mmap_read_lock(mm);
> +
> + addr = untagged_addr_remote(mm, args->shstk_token);
> + page = get_user_page_vma_remote(mm, addr, FOLL_FORCE | FOLL_WRITE,
> + &vma);
> + if (IS_ERR(page)) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (!(vma->vm_flags & VM_SHADOW_STACK) ||
> + !(vma->vm_flags & VM_WRITE)) {
> + ret = -EFAULT;
> + goto out_page;
> + }
> +
> + ret = arch_shstk_validate_clone(p, vma, page, args);
> +
> +out_page:
> + put_page(page);
> +out:
> + mmap_read_unlock(mm);
> + mmput(mm);
> + return ret;
> +}
> +
> /*
> * This creates a new process as a copy of the old one,
> * but does not actually start it yet.
> @@ -2182,6 +2227,9 @@ __latent_entropy struct task_struct *copy_process(
> if (retval)
> goto bad_fork_cleanup_namespaces;
> retval = copy_thread(p, args);
> + if (retval)
> + goto bad_fork_cleanup_io;
> + retval = shstk_validate_clone(p, args);
> if (retval)
> goto bad_fork_cleanup_io;
>
> @@ -2763,7 +2811,9 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> CLONE_ARGS_SIZE_VER1);
> BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
> CLONE_ARGS_SIZE_VER2);
> - BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
> + BUILD_BUG_ON(offsetofend(struct clone_args, shstk_token) !=
> + CLONE_ARGS_SIZE_VER3);
> + BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
>
> if (unlikely(usize > PAGE_SIZE))
> return -E2BIG;
> @@ -2796,16 +2846,17 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> return -EINVAL;
>
> *kargs = (struct kernel_clone_args){
> - .flags = args.flags,
> - .pidfd = u64_to_user_ptr(args.pidfd),
> - .child_tid = u64_to_user_ptr(args.child_tid),
> - .parent_tid = u64_to_user_ptr(args.parent_tid),
> - .exit_signal = args.exit_signal,
> - .stack = args.stack,
> - .stack_size = args.stack_size,
> - .tls = args.tls,
> - .set_tid_size = args.set_tid_size,
> - .cgroup = args.cgroup,
> + .flags = args.flags,
> + .pidfd = u64_to_user_ptr(args.pidfd),
> + .child_tid = u64_to_user_ptr(args.child_tid),
> + .parent_tid = u64_to_user_ptr(args.parent_tid),
> + .exit_signal = args.exit_signal,
> + .stack = args.stack,
> + .stack_size = args.stack_size,
> + .tls = args.tls,
> + .set_tid_size = args.set_tid_size,
> + .cgroup = args.cgroup,
> + .shstk_token = args.shstk_token,
> };
>
> if (args.set_tid &&
> @@ -2846,6 +2897,24 @@ static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
> return true;
> }
>
> +/**
> + * clone3_shadow_stack_valid - check and prepare shadow stack
> + * @kargs: kernel clone args
> + *
> + * Verify that shadow stacks are only enabled if supported.
> + */
> +static inline bool clone3_shadow_stack_valid(struct kernel_clone_args *kargs)
> +{
> + if (!kargs->shstk_token)
> + return true;
> +
> + if (!IS_ALIGNED(kargs->shstk_token, sizeof(void *)))
> + return false;
> +
> + /* Fail if the kernel wasn't built with shadow stacks */
> + return IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK);
> +}
> +
> static bool clone3_args_valid(struct kernel_clone_args *kargs)
> {
> /* Verify that no unknown flags are passed along. */
> @@ -2868,7 +2937,7 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
> kargs->exit_signal)
> return false;
>
> - if (!clone3_stack_valid(kargs))
> + if (!clone3_stack_valid(kargs) || !clone3_shadow_stack_valid(kargs))
> return false;
>
> return true;
>
> --
> 2.47.2
>
^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Jessica Clarke @ 2025-09-16 17:08 UTC (permalink / raw)
To: Askar Safin
Cc: linux-fsdevel, linux-kernel, Linus Torvalds, Greg Kroah-Hartman,
Christian Brauner, Al Viro, Jan Kara, Christoph Hellwig,
Jens Axboe, Andy Shevchenko, Aleksa Sarai, Thomas Weißschuh,
Julian Stecklina, Gao Xiang, Art Nikpal, Andrew Morton,
Eric Curtin, Alexander Graf, Rob Landley, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <20250913003842.41944-1-safinaskar@gmail.com>
On 13 Sep 2025, at 01:37, Askar Safin <safinaskar@gmail.com> wrote:
> [...]
> For example, I renamed the following global variables:
>
> __initramfs_start
> __initramfs_size
> [...]
>
> to:
>
> __builtin_initramfs_start
> __builtin_initramfs_size
I strongly suggest picking different names given __builtin_foo is the
naming scheme used for GNU C builtins/intrinsics. I leave you and
others to bikeshed that one.
Jessica
^ permalink raw reply
* [PATCH v2 3/3] ext4: implemet new ioctls to set and get superblock parameters
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
parameters to be set while the file system is mounted, without needing
write access to the block device.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
include/uapi/linux/ext4.h | 53 +++++++++++++
2 files changed, 358 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..a93a7baae990cc5580d2ddb3ffcc72fe15246978 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -27,14 +27,16 @@
#include "fsmap.h"
#include <trace/events/ext4.h>
-typedef void ext4_update_sb_callback(struct ext4_super_block *es,
- const void *arg);
+typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es,
+ const void *arg);
/*
* Superblock modification callback function for changing file system
* label
*/
-static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
/* Sanity check, this should never happen */
BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
@@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
* Superblock modification callback function for changing file system
* UUID.
*/
-static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
}
@@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
goto out_err;
lock_buffer(bh);
- func(es, arg);
+ func(sbi, es, arg);
ext4_superblock_csum_set(sb);
unlock_buffer(bh);
@@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
unlock_buffer(bh);
goto out_bh;
}
- func(es, arg);
+ func(EXT4_SB(sb), es, arg);
if (ext4_has_feature_metadata_csum(sb))
es->s_checksum = ext4_superblock_csum(es);
set_buffer_uptodate(bh);
@@ -1230,6 +1233,295 @@ static int ext4_ioctl_setuuid(struct file *filp,
return ret;
}
+
+#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
+ EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
+ EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
+ EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
+ EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
+ EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
+ EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
+ EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
+ EXT4_TUNE_FL_FORCE_FSCK | EXT4_TUNE_FL_ENCODING | \
+ EXT4_TUNE_FL_ENCODING_FLAGS)
+
+#define EXT4_TUNE_SET_COMPAT_SUPP \
+ (EXT4_FEATURE_COMPAT_DIR_INDEX | \
+ EXT4_FEATURE_COMPAT_STABLE_INODES)
+#define EXT4_TUNE_SET_INCOMPAT_SUPP \
+ (EXT4_FEATURE_INCOMPAT_EXTENTS | \
+ EXT4_FEATURE_INCOMPAT_EA_INODE | \
+ EXT4_FEATURE_INCOMPAT_ENCRYPT | \
+ EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
+ EXT4_FEATURE_INCOMPAT_LARGEDIR | \
+ EXT4_FEATURE_INCOMPAT_CASEFOLD)
+#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
+ (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
+ EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
+ EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
+ EXT4_FEATURE_RO_COMPAT_PROJECT | \
+ EXT4_FEATURE_RO_COMPAT_VERITY)
+
+#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP (0)
+
+#define SB_ENC_SUPP_MASK (SB_ENC_STRICT_MODE_FL | \
+ SB_ENC_NO_COMPAT_FALLBACK_FL)
+
+static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
+ struct ext4_tune_sb_params __user *params)
+{
+ struct ext4_tune_sb_params ret;
+ struct ext4_super_block *es = sbi->s_es;
+
+ memset(&ret, 0, sizeof(ret));
+ ret.set_flags = TUNE_OPS_SUPPORTED;
+ ret.errors_behavior = le16_to_cpu(es->s_errors);
+ ret.mnt_count = le16_to_cpu(es->s_mnt_count);
+ ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
+ ret.checkinterval = le32_to_cpu(es->s_checkinterval);
+ ret.last_check_time = le32_to_cpu(es->s_lastcheck);
+ ret.reserved_blocks = ext4_r_blocks_count(es);
+ ret.blocks_count = ext4_blocks_count(es);
+ ret.reserved_uid = ext4_get_resuid(es);
+ ret.reserved_gid = ext4_get_resgid(es);
+ ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
+ ret.def_hash_alg = es->s_def_hash_version;
+ ret.raid_stride = le16_to_cpu(es->s_raid_stride);
+ ret.raid_stripe_width = le32_to_cpu(es->s_raid_stripe_width);
+ ret.encoding = le16_to_cpu(es->s_encoding);
+ ret.encoding_flags = le16_to_cpu(es->s_encoding_flags);
+ strscpy_pad(ret.mount_opts, es->s_mount_opts);
+ ret.feature_compat = le32_to_cpu(es->s_feature_compat);
+ ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
+ ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
+ ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
+ ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
+ ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
+ ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
+ ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
+ ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
+ if (copy_to_user(params, &ret, sizeof(ret)))
+ return -EFAULT;
+ return 0;
+}
+
+static void ext4_sb_setparams(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
+{
+ const struct ext4_tune_sb_params *params = arg;
+
+ if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
+ es->s_errors = cpu_to_le16(params->errors_behavior);
+ if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
+ es->s_mnt_count = cpu_to_le16(params->mnt_count);
+ if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
+ es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
+ if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
+ es->s_checkinterval = cpu_to_le32(params->checkinterval);
+ if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
+ es->s_lastcheck = cpu_to_le32(params->last_check_time);
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
+ ext4_fsblk_t blk = params->reserved_blocks;
+
+ es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
+ es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
+ int uid = params->reserved_uid;
+
+ es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
+ es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
+ int gid = params->reserved_gid;
+
+ es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
+ es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
+ es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
+ if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ es->s_def_hash_version = params->def_hash_alg;
+ if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
+ es->s_raid_stride = cpu_to_le16(params->raid_stride);
+ if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
+ es->s_raid_stripe_width =
+ cpu_to_le32(params->raid_stripe_width);
+ if (params->set_flags & EXT4_TUNE_FL_ENCODING)
+ es->s_encoding = cpu_to_le16(params->encoding);
+ if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
+ es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
+ strscpy_pad(es->s_mount_opts, params->mount_opts);
+ if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+ es->s_feature_compat |=
+ cpu_to_le32(params->set_feature_compat_mask);
+ es->s_feature_incompat |=
+ cpu_to_le32(params->set_feature_incompat_mask);
+ es->s_feature_ro_compat |=
+ cpu_to_le32(params->set_feature_ro_compat_mask);
+ es->s_feature_compat &=
+ ~cpu_to_le32(params->clear_feature_compat_mask);
+ es->s_feature_incompat &=
+ ~cpu_to_le32(params->clear_feature_incompat_mask);
+ es->s_feature_ro_compat &=
+ ~cpu_to_le32(params->clear_feature_ro_compat_mask);
+ if (params->set_feature_compat_mask &
+ EXT4_FEATURE_COMPAT_DIR_INDEX)
+ es->s_def_hash_version = sbi->s_def_hash_version;
+ if (params->set_feature_incompat_mask &
+ EXT4_FEATURE_INCOMPAT_CSUM_SEED)
+ es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
+ }
+ if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
+ es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
+}
+
+static int ext4_ioctl_set_tune_sb(struct file *filp,
+ struct ext4_tune_sb_params __user *in)
+{
+ struct ext4_tune_sb_params params;
+ struct super_block *sb = file_inode(filp)->i_sb;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_super_block *es = sbi->s_es;
+ int enabling_casefold = 0;
+ int ret;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (copy_from_user(¶ms, in, sizeof(params)))
+ return -EFAULT;
+
+ if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
+ return -EOPNOTSUPP;
+
+ if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
+ (params.errors_behavior > EXT4_ERRORS_PANIC))
+ return -EINVAL;
+
+ if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
+ (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
+ return -EINVAL;
+ if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
+ ((params.def_hash_alg > DX_HASH_LAST) ||
+ (params.def_hash_alg == DX_HASH_SIPHASH)))
+ return -EINVAL;
+ if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
+ (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
+ return -EINVAL;
+
+ if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
+ params.set_feature_compat_mask =
+ params.feature_compat &
+ ~le32_to_cpu(es->s_feature_compat);
+ params.set_feature_incompat_mask =
+ params.feature_incompat &
+ ~le32_to_cpu(es->s_feature_incompat);
+ params.set_feature_ro_compat_mask =
+ params.feature_ro_compat &
+ ~le32_to_cpu(es->s_feature_ro_compat);
+ params.clear_feature_compat_mask =
+ ~params.feature_compat &
+ le32_to_cpu(es->s_feature_compat);
+ params.clear_feature_incompat_mask =
+ ~params.feature_incompat &
+ le32_to_cpu(es->s_feature_incompat);
+ params.clear_feature_ro_compat_mask =
+ ~params.feature_ro_compat &
+ le32_to_cpu(es->s_feature_ro_compat);
+ params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
+ }
+ if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+ if ((params.set_feature_compat_mask &
+ ~EXT4_TUNE_SET_COMPAT_SUPP) ||
+ (params.set_feature_incompat_mask &
+ ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
+ (params.set_feature_ro_compat_mask &
+ ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
+ (params.clear_feature_compat_mask &
+ ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
+ (params.clear_feature_incompat_mask &
+ ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
+ (params.clear_feature_ro_compat_mask &
+ ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
+ return -EOPNOTSUPP;
+
+ /*
+ * Filter out the features that are already set from
+ * the set_mask.
+ */
+ params.set_feature_compat_mask &=
+ ~le32_to_cpu(es->s_feature_compat);
+ params.set_feature_incompat_mask &=
+ ~le32_to_cpu(es->s_feature_incompat);
+ params.set_feature_ro_compat_mask &=
+ ~le32_to_cpu(es->s_feature_ro_compat);
+ if ((params.set_feature_incompat_mask &
+ EXT4_FEATURE_INCOMPAT_CASEFOLD)) {
+ enabling_casefold = 1;
+ if (!(params.set_flags & EXT4_TUNE_FL_ENCODING)) {
+ params.encoding = EXT4_ENC_UTF8_12_1;
+ params.set_flags |= EXT4_TUNE_FL_ENCODING;
+ }
+ if (!(params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)) {
+ params.encoding_flags = 0;
+ params.set_flags |= EXT4_TUNE_FL_ENCODING_FLAGS;
+ }
+ }
+ if ((params.set_feature_compat_mask &
+ EXT4_FEATURE_COMPAT_DIR_INDEX)) {
+ uuid_t uu;
+
+ memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
+ if (uuid_is_null(&uu))
+ generate_random_uuid((char *)
+ &sbi->s_hash_seed);
+ if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ sbi->s_def_hash_version = params.def_hash_alg;
+ else if (sbi->s_def_hash_version == 0)
+ sbi->s_def_hash_version = DX_HASH_HALF_MD4;
+ if (!(es->s_flags &
+ cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
+ !(es->s_flags &
+ cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
+#ifdef __CHAR_UNSIGNED__
+ sbi->s_hash_unsigned = 3;
+#else
+ sbi->s_hash_unsigned = 0;
+#endif
+ }
+ }
+ }
+ if (params.set_flags & EXT4_TUNE_FL_ENCODING) {
+ if (!enabling_casefold)
+ return -EINVAL;
+ if (params.encoding == 0)
+ params.encoding = EXT4_ENC_UTF8_12_1;
+ else if (params.encoding != EXT4_ENC_UTF8_12_1)
+ return -EINVAL;
+ }
+ if (params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS) {
+ if (!enabling_casefold)
+ return -EINVAL;
+ if (params.encoding_flags & ~SB_ENC_SUPP_MASK)
+ return -EINVAL;
+ }
+
+ ret = mnt_want_write_file(filp);
+ if (ret)
+ return ret;
+
+ ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
+ mnt_drop_write_file(filp);
+
+ if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+ sbi->s_def_hash_version = params.def_hash_alg;
+
+ return ret;
+}
+
static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct inode *inode = file_inode(filp);
@@ -1616,6 +1908,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
case EXT4_IOC_SETFSUUID:
return ext4_ioctl_setuuid(filp, (const void __user *)arg);
+ case EXT4_IOC_GET_TUNE_SB_PARAM:
+ return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
+ (void __user *)arg);
+ case EXT4_IOC_SET_TUNE_SB_PARAM:
+ return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
default:
return -ENOTTY;
}
@@ -1703,7 +2000,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}
#endif
-static void set_overhead(struct ext4_super_block *es, const void *arg)
+static void set_overhead(struct ext4_sb_info *sbi,
+ struct ext4_super_block *es, const void *arg)
{
es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
}
diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..411dcc1e4a35c8c6a10f3768d17b8cc50cff4c34 100644
--- a/include/uapi/linux/ext4.h
+++ b/include/uapi/linux/ext4.h
@@ -33,6 +33,8 @@
#define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
#define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
#define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
+#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
+#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
#define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
@@ -108,6 +110,57 @@ struct ext4_new_group_input {
__u16 unused;
};
+struct ext4_tune_sb_params {
+ __u32 set_flags;
+ __u32 checkinterval;
+ __u16 errors_behavior;
+ __u16 mnt_count;
+ __u16 max_mnt_count;
+ __u16 raid_stride;
+ __u64 last_check_time;
+ __u64 reserved_blocks;
+ __u64 blocks_count;
+ __u32 default_mnt_opts;
+ __u32 reserved_uid;
+ __u32 reserved_gid;
+ __u32 raid_stripe_width;
+ __u16 encoding;
+ __u16 encoding_flags;
+ __u8 def_hash_alg;
+ __u8 pad_1;
+ __u16 pad_2;
+ __u32 feature_compat;
+ __u32 feature_incompat;
+ __u32 feature_ro_compat;
+ __u32 set_feature_compat_mask;
+ __u32 set_feature_incompat_mask;
+ __u32 set_feature_ro_compat_mask;
+ __u32 clear_feature_compat_mask;
+ __u32 clear_feature_incompat_mask;
+ __u32 clear_feature_ro_compat_mask;
+ __u8 mount_opts[64];
+ __u8 pad[64];
+};
+
+#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
+#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
+#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
+#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
+#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
+#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
+#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
+#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
+#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
+#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
+#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
+#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
+#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
+#define EXT4_TUNE_FL_FEATURES 0x00002000
+#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
+#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
+#define EXT4_TUNE_FL_ENCODING 0x00010000
+#define EXT4_TUNE_FL_ENCODING_FLAGS 0x00020000
+
/*
* Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
* It indicates that the entry in extent status cache is for a hole.
--
2.51.0
^ permalink raw reply related
* [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Support for specifying the default user id and group id that is
allowed to use the reserved block space was added way back when Linux
only supported 16-bit uid's and gid's. (Yeah, that long ago.) It's
not a commonly used feature, but let's add support for 32-bit user and
group id's.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/ext4.h | 16 +++++++++++++++-
fs/ext4/super.c | 8 ++++----
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1442,7 +1442,9 @@ struct ext4_super_block {
__le16 s_encoding; /* Filename charset encoding */
__le16 s_encoding_flags; /* Filename charset encoding flags */
__le32 s_orphan_file_inum; /* Inode for tracking orphan inodes */
- __le32 s_reserved[94]; /* Padding to the end of the block */
+ __le16 s_def_resuid_hi;
+ __le16 s_def_resgid_hi;
+ __le32 s_reserved[93]; /* Padding to the end of the block */
__le32 s_checksum; /* crc32c(superblock) */
};
@@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
}
+static inline int ext4_get_resuid(struct ext4_super_block *es)
+{
+ return(le16_to_cpu(es->s_def_resuid) |
+ (le16_to_cpu(es->s_def_resuid_hi) << 16));
+}
+
+static inline int ext4_get_resgid(struct ext4_super_block *es)
+{
+ return(le16_to_cpu(es->s_def_resgid) |
+ (le16_to_cpu(es->s_def_resgid_hi) << 16));
+}
+
/*
* Returns: sbi->field[index]
* Used to access an array element from the following sbi fields which require
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
}
if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
- le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
+ ext4_get_resuid(es) != EXT4_DEF_RESUID)
SEQ_OPTS_PRINT("resuid=%u",
from_kuid_munged(&init_user_ns, sbi->s_resuid));
if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
- le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
+ ext4_get_resgid(es) != EXT4_DEF_RESGID)
SEQ_OPTS_PRINT("resgid=%u",
from_kgid_munged(&init_user_ns, sbi->s_resgid));
def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
@@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
ext4_set_def_opts(sb, es);
- sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
- sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
+ sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
+ sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
--
2.51.0
^ permalink raw reply related
* [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
In-Reply-To: <20250916-tune2fs-v2-0-d594dc7486f0@mit.edu>
From: Theodore Ts'o <tytso@mit.edu>
Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated. Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.
Cc: stable@vger.kernel.org
Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/super.c | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
struct ext4_fs_context *m_ctx)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
- char *s_mount_opts = NULL;
+ char s_mount_opts[65];
struct ext4_fs_context *s_ctx = NULL;
struct fs_context *fc = NULL;
int ret = -ENOMEM;
@@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
if (!sbi->s_es->s_mount_opts[0])
return 0;
- s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
- sizeof(sbi->s_es->s_mount_opts),
- GFP_KERNEL);
- if (!s_mount_opts)
- return ret;
+ strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
if (!fc)
- goto out_free;
+ return -ENOMEM;
s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
if (!s_ctx)
@@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
ret = 0;
out_free:
- if (fc) {
- ext4_fc_free(fc);
- kfree(fc);
- }
- kfree(s_mount_opts);
+ ext4_fc_free(fc);
+ kfree(fc);
return ret;
}
--
2.51.0
^ permalink raw reply related
* [PATCH v2 0/3] ext4: Add support for mounted updates to the superblock via an ioctl
From: Theodore Ts'o via B4 Relay @ 2025-09-17 3:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
This patch series enables a future version of tune2fs to be able to
modify certain parts of the ext4 superblock without to write to the
block device.
The first patch fixes a potential buffer overrun caused by a
maliciously moified superblock. The second patch adds support for
32-bit uid and gid's which can have access to the reserved blocks pool.
The last patch adds the ioctl's which will be used by tune2fs.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
Changes in v2:
- fix bugs that were detected using sparse
- remove tune (unsafe) ability to clear certain compat faatures
- add the ability to set the encoding and encoding flags for case folding
- Link to v1: https://lore.kernel.org/r/20250908-tune2fs-v1-0-e3a6929f3355@mit.edu
---
Theodore Ts'o (3):
ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
ext4: add support for 32-bit default reserved uid and gid values
ext4: implemet new ioctls to set and get superblock parameters
fs/ext4/ext4.h | 16 +++-
fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
fs/ext4/super.c | 25 +++----
include/uapi/linux/ext4.h | 53 +++++++++++++
4 files changed, 382 insertions(+), 24 deletions(-)
---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250830-tune2fs-3376beb72403
Best regards,
--
Theodore Ts'o <tytso@mit.edu>
^ permalink raw reply
* Re: [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: Jan Kara @ 2025-09-17 16:05 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api, stable
In-Reply-To: <20250916-tune2fs-v2-1-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:47, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Unlike other strings in the ext4 superblock, we rely on tune2fs to
> make sure s_mount_opts is NUL terminated. Harden
> parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> __nonstring.
>
> Cc: stable@vger.kernel.org
> Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/ext4/super.c | 17 +++++------------
> 1 file changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> struct ext4_fs_context *m_ctx)
> {
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> - char *s_mount_opts = NULL;
> + char s_mount_opts[65];
> struct ext4_fs_context *s_ctx = NULL;
> struct fs_context *fc = NULL;
> int ret = -ENOMEM;
> @@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> if (!sbi->s_es->s_mount_opts[0])
> return 0;
>
> - s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> - sizeof(sbi->s_es->s_mount_opts),
> - GFP_KERNEL);
> - if (!s_mount_opts)
> - return ret;
> + strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
>
> fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
> if (!fc)
> - goto out_free;
> + return -ENOMEM;
>
> s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
> if (!s_ctx)
> @@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> ret = 0;
>
> out_free:
> - if (fc) {
> - ext4_fc_free(fc);
> - kfree(fc);
> - }
> - kfree(s_mount_opts);
> + ext4_fc_free(fc);
> + kfree(fc);
> return ret;
> }
>
>
> --
> 2.51.0
>
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values
From: Jan Kara @ 2025-09-17 16:10 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-2-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:48, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Support for specifying the default user id and group id that is
> allowed to use the reserved block space was added way back when Linux
> only supported 16-bit uid's and gid's. (Yeah, that long ago.) It's
> not a commonly used feature, but let's add support for 32-bit user and
> group id's.
>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
> fs/ext4/ext4.h | 16 +++++++++++++++-
> fs/ext4/super.c | 8 ++++----
> 2 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1442,7 +1442,9 @@ struct ext4_super_block {
> __le16 s_encoding; /* Filename charset encoding */
> __le16 s_encoding_flags; /* Filename charset encoding flags */
> __le32 s_orphan_file_inum; /* Inode for tracking orphan inodes */
> - __le32 s_reserved[94]; /* Padding to the end of the block */
> + __le16 s_def_resuid_hi;
> + __le16 s_def_resgid_hi;
> + __le32 s_reserved[93]; /* Padding to the end of the block */
> __le32 s_checksum; /* crc32c(superblock) */
> };
>
> @@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
> ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
> }
>
> +static inline int ext4_get_resuid(struct ext4_super_block *es)
> +{
> + return(le16_to_cpu(es->s_def_resuid) |
> + (le16_to_cpu(es->s_def_resuid_hi) << 16));
> +}
I'd prefer a style like:
return le16_to_cpu(es->s_def_resuid) |
(le16_to_cpu(es->s_def_resuid_hi) << 16);
but whatever...
> @@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>
> ext4_set_def_opts(sb, es);
>
> - sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
> - sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
> + sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
> + sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
^^^^ ext4_get_resgid() here.
> sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
> sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
> sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH v2 3/3] ext4: implemet new ioctls to set and get superblock parameters
From: Jan Kara @ 2025-09-17 16:22 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-3-d594dc7486f0@mit.edu>
On Tue 16-09-25 23:22:49, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
> EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
> parameters to be set while the file system is mounted, without needing
> write access to the block device.
>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> include/uapi/linux/ext4.h | 53 +++++++++++++
> 2 files changed, 358 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..a93a7baae990cc5580d2ddb3ffcc72fe15246978 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -27,14 +27,16 @@
> #include "fsmap.h"
> #include <trace/events/ext4.h>
>
> -typedef void ext4_update_sb_callback(struct ext4_super_block *es,
> - const void *arg);
> +typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es,
> + const void *arg);
>
> /*
> * Superblock modification callback function for changing file system
> * label
> */
> -static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> /* Sanity check, this should never happen */
> BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
> @@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> * Superblock modification callback function for changing file system
> * UUID.
> */
> -static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
> }
> @@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
> goto out_err;
>
> lock_buffer(bh);
> - func(es, arg);
> + func(sbi, es, arg);
> ext4_superblock_csum_set(sb);
> unlock_buffer(bh);
>
> @@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
> unlock_buffer(bh);
> goto out_bh;
> }
> - func(es, arg);
> + func(EXT4_SB(sb), es, arg);
> if (ext4_has_feature_metadata_csum(sb))
> es->s_checksum = ext4_superblock_csum(es);
> set_buffer_uptodate(bh);
> @@ -1230,6 +1233,295 @@ static int ext4_ioctl_setuuid(struct file *filp,
> return ret;
> }
>
> +
> +#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
> + EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
> + EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
> + EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
> + EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
> + EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
> + EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
> + EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
> + EXT4_TUNE_FL_FORCE_FSCK | EXT4_TUNE_FL_ENCODING | \
> + EXT4_TUNE_FL_ENCODING_FLAGS)
> +
> +#define EXT4_TUNE_SET_COMPAT_SUPP \
> + (EXT4_FEATURE_COMPAT_DIR_INDEX | \
> + EXT4_FEATURE_COMPAT_STABLE_INODES)
> +#define EXT4_TUNE_SET_INCOMPAT_SUPP \
> + (EXT4_FEATURE_INCOMPAT_EXTENTS | \
> + EXT4_FEATURE_INCOMPAT_EA_INODE | \
> + EXT4_FEATURE_INCOMPAT_ENCRYPT | \
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
> + EXT4_FEATURE_INCOMPAT_LARGEDIR | \
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)
> +#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
> + (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
> + EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
> + EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
> + EXT4_FEATURE_RO_COMPAT_PROJECT | \
> + EXT4_FEATURE_RO_COMPAT_VERITY)
> +
> +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP (0)
> +
> +#define SB_ENC_SUPP_MASK (SB_ENC_STRICT_MODE_FL | \
> + SB_ENC_NO_COMPAT_FALLBACK_FL)
> +
> +static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
> + struct ext4_tune_sb_params __user *params)
> +{
> + struct ext4_tune_sb_params ret;
> + struct ext4_super_block *es = sbi->s_es;
> +
> + memset(&ret, 0, sizeof(ret));
> + ret.set_flags = TUNE_OPS_SUPPORTED;
> + ret.errors_behavior = le16_to_cpu(es->s_errors);
> + ret.mnt_count = le16_to_cpu(es->s_mnt_count);
> + ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
> + ret.checkinterval = le32_to_cpu(es->s_checkinterval);
> + ret.last_check_time = le32_to_cpu(es->s_lastcheck);
> + ret.reserved_blocks = ext4_r_blocks_count(es);
> + ret.blocks_count = ext4_blocks_count(es);
> + ret.reserved_uid = ext4_get_resuid(es);
> + ret.reserved_gid = ext4_get_resgid(es);
> + ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
> + ret.def_hash_alg = es->s_def_hash_version;
> + ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> + ret.raid_stripe_width = le32_to_cpu(es->s_raid_stripe_width);
> + ret.encoding = le16_to_cpu(es->s_encoding);
> + ret.encoding_flags = le16_to_cpu(es->s_encoding_flags);
> + strscpy_pad(ret.mount_opts, es->s_mount_opts);
> + ret.feature_compat = le32_to_cpu(es->s_feature_compat);
> + ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
> + ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
> + ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
> + ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
> + ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
> + ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
> + ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
> + ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
> + if (copy_to_user(params, &ret, sizeof(ret)))
> + return -EFAULT;
> + return 0;
> +}
> +
> +static void ext4_sb_setparams(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> +{
> + const struct ext4_tune_sb_params *params = arg;
> +
> + if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
> + es->s_errors = cpu_to_le16(params->errors_behavior);
> + if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
> + es->s_mnt_count = cpu_to_le16(params->mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
> + es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
> + es->s_checkinterval = cpu_to_le32(params->checkinterval);
> + if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
> + es->s_lastcheck = cpu_to_le32(params->last_check_time);
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
> + ext4_fsblk_t blk = params->reserved_blocks;
> +
> + es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
> + es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
> + int uid = params->reserved_uid;
> +
> + es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
> + es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
> + int gid = params->reserved_gid;
> +
> + es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
> + es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
> + es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
> + if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + es->s_def_hash_version = params->def_hash_alg;
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
> + es->s_raid_stride = cpu_to_le16(params->raid_stride);
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> + es->s_raid_stripe_width =
> + cpu_to_le32(params->raid_stripe_width);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING)
> + es->s_encoding = cpu_to_le16(params->encoding);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
> + es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
> + strscpy_pad(es->s_mount_opts, params->mount_opts);
> + if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + es->s_feature_compat |=
> + cpu_to_le32(params->set_feature_compat_mask);
> + es->s_feature_incompat |=
> + cpu_to_le32(params->set_feature_incompat_mask);
> + es->s_feature_ro_compat |=
> + cpu_to_le32(params->set_feature_ro_compat_mask);
> + es->s_feature_compat &=
> + ~cpu_to_le32(params->clear_feature_compat_mask);
> + es->s_feature_incompat &=
> + ~cpu_to_le32(params->clear_feature_incompat_mask);
> + es->s_feature_ro_compat &=
> + ~cpu_to_le32(params->clear_feature_ro_compat_mask);
> + if (params->set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)
> + es->s_def_hash_version = sbi->s_def_hash_version;
> + if (params->set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED)
> + es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
> + es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
> +}
> +
> +static int ext4_ioctl_set_tune_sb(struct file *filp,
> + struct ext4_tune_sb_params __user *in)
> +{
> + struct ext4_tune_sb_params params;
> + struct super_block *sb = file_inode(filp)->i_sb;
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct ext4_super_block *es = sbi->s_es;
> + int enabling_casefold = 0;
> + int ret;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (copy_from_user(¶ms, in, sizeof(params)))
> + return -EFAULT;
> +
> + if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
> + return -EOPNOTSUPP;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
> + (params.errors_behavior > EXT4_ERRORS_PANIC))
> + return -EINVAL;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
> + (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
> + ((params.def_hash_alg > DX_HASH_LAST) ||
> + (params.def_hash_alg == DX_HASH_SIPHASH)))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
> + (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
> + return -EINVAL;
> +
> + if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
> + params.set_feature_compat_mask =
> + params.feature_compat &
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask =
> + params.feature_incompat &
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask =
> + params.feature_ro_compat &
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + params.clear_feature_compat_mask =
> + ~params.feature_compat &
> + le32_to_cpu(es->s_feature_compat);
> + params.clear_feature_incompat_mask =
> + ~params.feature_incompat &
> + le32_to_cpu(es->s_feature_incompat);
> + params.clear_feature_ro_compat_mask =
> + ~params.feature_ro_compat &
> + le32_to_cpu(es->s_feature_ro_compat);
> + params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + if ((params.set_feature_compat_mask &
> + ~EXT4_TUNE_SET_COMPAT_SUPP) ||
> + (params.set_feature_incompat_mask &
> + ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
> + (params.set_feature_ro_compat_mask &
> + ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
> + (params.clear_feature_compat_mask &
> + ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
> + (params.clear_feature_incompat_mask &
> + ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
> + (params.clear_feature_ro_compat_mask &
> + ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
> + return -EOPNOTSUPP;
> +
> + /*
> + * Filter out the features that are already set from
> + * the set_mask.
> + */
> + params.set_feature_compat_mask &=
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask &=
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask &=
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + if ((params.set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)) {
> + enabling_casefold = 1;
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING)) {
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING;
> + }
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)) {
> + params.encoding_flags = 0;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING_FLAGS;
> + }
> + }
> + if ((params.set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)) {
> + uuid_t uu;
> +
> + memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
> + if (uuid_is_null(&uu))
> + generate_random_uuid((char *)
> + &sbi->s_hash_seed);
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> + else if (sbi->s_def_hash_version == 0)
> + sbi->s_def_hash_version = DX_HASH_HALF_MD4;
> + if (!(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
> + !(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
> +#ifdef __CHAR_UNSIGNED__
> + sbi->s_hash_unsigned = 3;
> +#else
> + sbi->s_hash_unsigned = 0;
> +#endif
> + }
> + }
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding == 0)
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + else if (params.encoding != EXT4_ENC_UTF8_12_1)
> + return -EINVAL;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding_flags & ~SB_ENC_SUPP_MASK)
> + return -EINVAL;
> + }
> +
> + ret = mnt_want_write_file(filp);
> + if (ret)
> + return ret;
> +
> + ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
> + mnt_drop_write_file(filp);
> +
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> +
> + return ret;
> +}
> +
> static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> struct inode *inode = file_inode(filp);
> @@ -1616,6 +1908,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
> case EXT4_IOC_SETFSUUID:
> return ext4_ioctl_setuuid(filp, (const void __user *)arg);
> + case EXT4_IOC_GET_TUNE_SB_PARAM:
> + return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
> + (void __user *)arg);
> + case EXT4_IOC_SET_TUNE_SB_PARAM:
> + return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
> default:
> return -ENOTTY;
> }
> @@ -1703,7 +2000,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> }
> #endif
>
> -static void set_overhead(struct ext4_super_block *es, const void *arg)
> +static void set_overhead(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
> }
> diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
> index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..411dcc1e4a35c8c6a10f3768d17b8cc50cff4c34 100644
> --- a/include/uapi/linux/ext4.h
> +++ b/include/uapi/linux/ext4.h
> @@ -33,6 +33,8 @@
> #define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
> #define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
> #define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
> +#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
>
> #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
>
> @@ -108,6 +110,57 @@ struct ext4_new_group_input {
> __u16 unused;
> };
>
> +struct ext4_tune_sb_params {
> + __u32 set_flags;
> + __u32 checkinterval;
> + __u16 errors_behavior;
> + __u16 mnt_count;
> + __u16 max_mnt_count;
> + __u16 raid_stride;
> + __u64 last_check_time;
> + __u64 reserved_blocks;
> + __u64 blocks_count;
> + __u32 default_mnt_opts;
> + __u32 reserved_uid;
> + __u32 reserved_gid;
> + __u32 raid_stripe_width;
> + __u16 encoding;
> + __u16 encoding_flags;
> + __u8 def_hash_alg;
> + __u8 pad_1;
> + __u16 pad_2;
> + __u32 feature_compat;
> + __u32 feature_incompat;
> + __u32 feature_ro_compat;
> + __u32 set_feature_compat_mask;
> + __u32 set_feature_incompat_mask;
> + __u32 set_feature_ro_compat_mask;
> + __u32 clear_feature_compat_mask;
> + __u32 clear_feature_incompat_mask;
> + __u32 clear_feature_ro_compat_mask;
> + __u8 mount_opts[64];
> + __u8 pad[64];
> +};
> +
> +#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
> +#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
> +#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
> +#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
> +#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
> +#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
> +#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
> +#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
> +#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
> +#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
> +#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
> +#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
> +#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
> +#define EXT4_TUNE_FL_FEATURES 0x00002000
> +#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
> +#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
> +#define EXT4_TUNE_FL_ENCODING 0x00010000
> +#define EXT4_TUNE_FL_ENCODING_FLAGS 0x00020000
> +
> /*
> * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
> * It indicates that the entry in extent status cache is for a hole.
>
> --
> 2.51.0
>
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply
* Re: [PATCH 00/62] initrd: remove classic initrd support
From: Andy Lutomirski @ 2025-09-17 18:00 UTC (permalink / raw)
To: Rob Landley
Cc: Askar Safin, linux-fsdevel, linux-kernel, Linus Torvalds,
Greg Kroah-Hartman, Christian Brauner, Al Viro, Jan Kara,
Christoph Hellwig, Jens Axboe, Andy Shevchenko, Aleksa Sarai,
Thomas Weißschuh, Julian Stecklina, Gao Xiang, Art Nikpal,
Andrew Morton, Eric Curtin, Alexander Graf, Lennart Poettering,
linux-arch, linux-alpha, linux-snps-arc, linux-arm-kernel,
linux-csky, linux-hexagon, loongarch, linux-m68k, linux-mips,
linux-openrisc, linux-parisc, linuxppc-dev, linux-riscv,
linux-s390, linux-sh, sparclinux, linux-um, x86, Ingo Molnar,
linux-block, initramfs, linux-api, linux-doc, linux-efi,
linux-ext4, Theodore Y . Ts'o, linux-acpi, Michal Simek,
devicetree, Luis Chamberlain, Kees Cook, Thorsten Blum,
Heiko Carstens, patches
In-Reply-To: <0342fbda-9901-4293-afa7-ba6085eb1688@landley.net>
On Mon, Sep 15, 2025 at 10:09 AM Rob Landley <rob@landley.net> wrote:
> While you're at it, could you fix static/builtin initramfs so PID 1 has
> a valid stdin/stdout/stderr?
>
> A static initramfs won't create /dev/console if the embedded initramfs
> image doesn't contain it, which a non-root build can't mknod, so the
> kernel plumbing won't see it dev in the directory we point it at unless
> we build with root access.
I have no current insight as to whether there's a kernel issue here,
but why are you trying to put actual device nodes in an actual
filesystem as part of a build process? It's extremely straightforward
to emit devices nodes in cpio format, and IMO it's far *more*
straightforward to do that than to make a whole directory, try to get
all the modes right, and cpio it up.
I wrote an absolutely trivial tool for this several years ago:
https://github.com/amluto/virtme/blob/master/virtme/cpiowriter.py
it would be barely more complicated to strip the trailer off an cpio
file from some other source, add some device nodes, and stick the
trailer back on. But it's also really, really, really easy to emit an
entire, functioning cpio-formatted initramfs from plain user code with
no filesystem manipulation at all. This also makes that portion of
the build reproducible, which is worth quite a bit IMO.
--Andy
^ permalink raw reply
* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Will Deacon @ 2025-09-18 12:38 UTC (permalink / raw)
To: Mark Brown, brauner
Cc: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Shuah Khan, linux-kernel,
Catalin Marinas, jannh, Andrew Morton, Yury Khrustalev,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook
In-Reply-To: <20250916-clone3-shadow-stack-v21-4-910493527013@kernel.org>
On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the shadow
> stack for a new thread, instead the kernel will dynamically allocate a
> new shadow stack with the same size as the normal stack. This appears to
> be due to the shadow stack series having been in development since
> before the more extensible clone3() was added rather than anything more
> deliberate.
>
> Add a parameter to clone3() specifying a shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active. If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
>
> If a shadow stack pointer is specified then it is required to have an
> architecture defined token placed on the stack, this will be consumed by
> the new task, the shadow stack is specified by pointing to this token. If
> no valid token is present then this will be reported with -EINVAL. This
> token prevents new threads being created pointing at the shadow stack of
> an existing running thread. On architectures with support for userspace
> pivoting of shadow stacks it is expected that the same format and placement
> of tokens will be used, this is the case for arm64 and x86.
>
> If the architecture does not support shadow stacks the shadow stack
> pointer must be not be specified, architectures that do support the
> feature are expected to enforce the same requirement on individual
> systems that lack shadow stack support.
>
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
>
> Portions of the x86 architecture code were written by Rick Edgecombe.
>
> Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
> arch/x86/include/asm/shstk.h | 11 +++--
> arch/x86/kernel/process.c | 2 +-
> arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
> include/asm-generic/cacheflush.h | 11 +++++
> include/linux/sched/task.h | 17 ++++++++
> include/uapi/linux/sched.h | 9 ++--
> kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
> 8 files changed, 217 insertions(+), 26 deletions(-)
It would be great if Christian could give this the thumbs up, given that
it changes clone3(). I think the architecture parts are all ready at this
point.
Will
^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Nicolas Schichan @ 2025-09-18 15:28 UTC (permalink / raw)
To: safinaskar
Cc: akpm, andy.shevchenko, axboe, brauner, cyphar, devicetree,
ecurtin, email2tema, graf, gregkh, hca, hch, hsiangkao, initramfs,
jack, julian.stecklina, kees, linux-acpi, linux-alpha, linux-api,
linux-arch, linux-arm-kernel, linux-block, linux-csky, linux-doc,
linux-efi, linux-ext4, linux-fsdevel, linux-hexagon, linux-kernel,
linux-m68k, linux-mips, linux-openrisc, linux-parisc, linux-riscv,
linux-s390, linux-sh, linux-snps-arc, linux-um, linuxppc-dev,
loongarch, mcgrof, mingo, monstr, mzxreary, patches, rob,
sparclinux, thomas.weissschuh, thorsten.blum, torvalds, tytso,
viro, x86, nschichan
In-Reply-To: <20250913003842.41944-1-safinaskar@gmail.com>
Hello,
> Intro
> ====
> This patchset removes classic initrd (initial RAM disk) support,
> which was deprecated in 2020.
This serie came a bit as a surprise, because even though the message
notifying of the initrd deprecation was added in July 2020, the message
was never displayed on our kernels.
When booting with root=/dev/ram0 in the kernel commandline,
handle_initrd() where the deprecation message resides is never called,
which is rather unfortunate (init/do_mounts_initrd.c):
if (rd_load_image("/initrd.image") && ROOT_DEV != Root_RAM0) {
init_unlink("/initrd.image");
handle_initrd(root_device_name); // shows the deprecation msg
return true;
}
It is likely we are not the alone booting with that particular
configuration, so other people are probably going to be surprised when
initrd support is removed, because they never saw the deprecation
message.
We do depend on initrd support a lot on our embedded platforms (more
than a million devices with a yearlyish upgrade to the latest
kernel). If it eventually becomes removed this is going to impact us.
We use an initrd squashfs4 image, because coming from a time where
embedded flash devices were fragile, we avoid having the root
filesystem directly mounted (even when read only) on the flash
block/mtd device, and have the bootloader load the root filesystem as
an initrd.
We use a squashfs4 because we can mount it and keep it compressed. The
kernel would decompress data on demand in the page cache, and evict it
as needed.
Regards,
--
Nicolas Schichan
^ permalink raw reply
* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Will Deacon @ 2025-09-18 16:04 UTC (permalink / raw)
To: Mark Brown, brauner
Cc: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Shuah Khan, linux-kernel,
Catalin Marinas, jannh, Andrew Morton, Yury Khrustalev,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook
In-Reply-To: <aMv9XRq_sAQbQwjI@willie-the-truck>
On Thu, Sep 18, 2025 at 01:38:53PM +0100, Will Deacon wrote:
> On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> > Unlike with the normal stack there is no API for configuring the shadow
> > stack for a new thread, instead the kernel will dynamically allocate a
> > new shadow stack with the same size as the normal stack. This appears to
> > be due to the shadow stack series having been in development since
> > before the more extensible clone3() was added rather than anything more
> > deliberate.
> >
> > Add a parameter to clone3() specifying a shadow stack pointer to use
> > for the new thread, this is inconsistent with the way we specify the
> > normal stack but during review concerns were expressed about having to
> > identify where the shadow stack pointer should be placed especially in
> > cases where the shadow stack has been previously active. If no shadow
> > stack is specified then the existing implicit allocation behaviour is
> > maintained.
> >
> > If a shadow stack pointer is specified then it is required to have an
> > architecture defined token placed on the stack, this will be consumed by
> > the new task, the shadow stack is specified by pointing to this token. If
> > no valid token is present then this will be reported with -EINVAL. This
> > token prevents new threads being created pointing at the shadow stack of
> > an existing running thread. On architectures with support for userspace
> > pivoting of shadow stacks it is expected that the same format and placement
> > of tokens will be used, this is the case for arm64 and x86.
> >
> > If the architecture does not support shadow stacks the shadow stack
> > pointer must be not be specified, architectures that do support the
> > feature are expected to enforce the same requirement on individual
> > systems that lack shadow stack support.
> >
> > Update the existing arm64 and x86 implementations to pay attention to
> > the newly added arguments, in order to maintain compatibility we use the
> > existing behaviour if no shadow stack is specified. Since we are now
> > using more fields from the kernel_clone_args we pass that into the
> > shadow stack code rather than individual fields.
> >
> > Portions of the x86 architecture code were written by Rick Edgecombe.
> >
> > Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
> > Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Mark Brown <broonie@kernel.org>
> > ---
> > arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
> > arch/x86/include/asm/shstk.h | 11 +++--
> > arch/x86/kernel/process.c | 2 +-
> > arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
> > include/asm-generic/cacheflush.h | 11 +++++
> > include/linux/sched/task.h | 17 ++++++++
> > include/uapi/linux/sched.h | 9 ++--
> > kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
> > 8 files changed, 217 insertions(+), 26 deletions(-)
>
> It would be great if Christian could give this the thumbs up, given that
> it changes clone3(). I think the architecture parts are all ready at this
> point.
ah, I may have spoken too soon :/
Catalin pointed me at this glibc thread:
https://marc.info/?l=glibc-alpha&m=175811917427562
which sounds like they're not entirely on board with the new ABI.
Will
^ permalink raw reply
* Re: [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: Darrick J. Wong @ 2025-09-18 16:55 UTC (permalink / raw)
To: Jan Kara; +Cc: tytso, linux-ext4, linux-api, stable
In-Reply-To: <ik565ztp7s7zyhiog6n52zxylybtkkael6opfrmtvtf6su34iw@zho5dlhfvibq>
On Wed, Sep 17, 2025 at 06:05:06PM +0200, Jan Kara wrote:
> On Tue 16-09-25 23:22:47, Theodore Ts'o via B4 Relay wrote:
> > From: Theodore Ts'o <tytso@mit.edu>
> >
> > Unlike other strings in the ext4 superblock, we rely on tune2fs to
> > make sure s_mount_opts is NUL terminated. Harden
> > parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> > __nonstring.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
> > Signed-off-by: Theodore Ts'o <tytso@mit.edu>
>
> Looks good. Feel free to add:
>
> Reviewed-by: Jan Kara <jack@suse.cz>
Looks fine to me too,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
--D
>
> Honza
>
> > ---
> > fs/ext4/super.c | 17 +++++------------
> > 1 file changed, 5 insertions(+), 12 deletions(-)
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> > struct ext4_fs_context *m_ctx)
> > {
> > struct ext4_sb_info *sbi = EXT4_SB(sb);
> > - char *s_mount_opts = NULL;
> > + char s_mount_opts[65];
> > struct ext4_fs_context *s_ctx = NULL;
> > struct fs_context *fc = NULL;
> > int ret = -ENOMEM;
> > @@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> > if (!sbi->s_es->s_mount_opts[0])
> > return 0;
> >
> > - s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> > - sizeof(sbi->s_es->s_mount_opts),
> > - GFP_KERNEL);
> > - if (!s_mount_opts)
> > - return ret;
> > + strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
> >
> > fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
> > if (!fc)
> > - goto out_free;
> > + return -ENOMEM;
> >
> > s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
> > if (!s_ctx)
> > @@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> > ret = 0;
> >
> > out_free:
> > - if (fc) {
> > - ext4_fc_free(fc);
> > - kfree(fc);
> > - }
> > - kfree(s_mount_opts);
> > + ext4_fc_free(fc);
> > + kfree(fc);
> > return ret;
> > }
> >
> >
> > --
> > 2.51.0
> >
> >
> >
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
>
^ permalink raw reply
* Re: [PATCH v2 3/3] ext4: implemet new ioctls to set and get superblock parameters
From: Darrick J. Wong @ 2025-09-18 16:57 UTC (permalink / raw)
To: tytso; +Cc: linux-ext4, linux-api
In-Reply-To: <20250916-tune2fs-v2-3-d594dc7486f0@mit.edu>
On Tue, Sep 16, 2025 at 11:22:49PM -0400, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
>
> Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
> EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
> parameters to be set while the file system is mounted, without needing
> write access to the block device.
>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Looks good to me now,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
--D
> ---
> fs/ext4/ioctl.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> include/uapi/linux/ext4.h | 53 +++++++++++++
> 2 files changed, 358 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..a93a7baae990cc5580d2ddb3ffcc72fe15246978 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -27,14 +27,16 @@
> #include "fsmap.h"
> #include <trace/events/ext4.h>
>
> -typedef void ext4_update_sb_callback(struct ext4_super_block *es,
> - const void *arg);
> +typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es,
> + const void *arg);
>
> /*
> * Superblock modification callback function for changing file system
> * label
> */
> -static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> /* Sanity check, this should never happen */
> BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
> @@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> * Superblock modification callback function for changing file system
> * UUID.
> */
> -static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
> }
> @@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
> goto out_err;
>
> lock_buffer(bh);
> - func(es, arg);
> + func(sbi, es, arg);
> ext4_superblock_csum_set(sb);
> unlock_buffer(bh);
>
> @@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
> unlock_buffer(bh);
> goto out_bh;
> }
> - func(es, arg);
> + func(EXT4_SB(sb), es, arg);
> if (ext4_has_feature_metadata_csum(sb))
> es->s_checksum = ext4_superblock_csum(es);
> set_buffer_uptodate(bh);
> @@ -1230,6 +1233,295 @@ static int ext4_ioctl_setuuid(struct file *filp,
> return ret;
> }
>
> +
> +#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
> + EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
> + EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
> + EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
> + EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
> + EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
> + EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
> + EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
> + EXT4_TUNE_FL_FORCE_FSCK | EXT4_TUNE_FL_ENCODING | \
> + EXT4_TUNE_FL_ENCODING_FLAGS)
> +
> +#define EXT4_TUNE_SET_COMPAT_SUPP \
> + (EXT4_FEATURE_COMPAT_DIR_INDEX | \
> + EXT4_FEATURE_COMPAT_STABLE_INODES)
> +#define EXT4_TUNE_SET_INCOMPAT_SUPP \
> + (EXT4_FEATURE_INCOMPAT_EXTENTS | \
> + EXT4_FEATURE_INCOMPAT_EA_INODE | \
> + EXT4_FEATURE_INCOMPAT_ENCRYPT | \
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
> + EXT4_FEATURE_INCOMPAT_LARGEDIR | \
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)
> +#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
> + (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
> + EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
> + EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
> + EXT4_FEATURE_RO_COMPAT_PROJECT | \
> + EXT4_FEATURE_RO_COMPAT_VERITY)
> +
> +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP (0)
> +
> +#define SB_ENC_SUPP_MASK (SB_ENC_STRICT_MODE_FL | \
> + SB_ENC_NO_COMPAT_FALLBACK_FL)
> +
> +static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
> + struct ext4_tune_sb_params __user *params)
> +{
> + struct ext4_tune_sb_params ret;
> + struct ext4_super_block *es = sbi->s_es;
> +
> + memset(&ret, 0, sizeof(ret));
> + ret.set_flags = TUNE_OPS_SUPPORTED;
> + ret.errors_behavior = le16_to_cpu(es->s_errors);
> + ret.mnt_count = le16_to_cpu(es->s_mnt_count);
> + ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
> + ret.checkinterval = le32_to_cpu(es->s_checkinterval);
> + ret.last_check_time = le32_to_cpu(es->s_lastcheck);
> + ret.reserved_blocks = ext4_r_blocks_count(es);
> + ret.blocks_count = ext4_blocks_count(es);
> + ret.reserved_uid = ext4_get_resuid(es);
> + ret.reserved_gid = ext4_get_resgid(es);
> + ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
> + ret.def_hash_alg = es->s_def_hash_version;
> + ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> + ret.raid_stripe_width = le32_to_cpu(es->s_raid_stripe_width);
> + ret.encoding = le16_to_cpu(es->s_encoding);
> + ret.encoding_flags = le16_to_cpu(es->s_encoding_flags);
> + strscpy_pad(ret.mount_opts, es->s_mount_opts);
> + ret.feature_compat = le32_to_cpu(es->s_feature_compat);
> + ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
> + ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
> + ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
> + ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
> + ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
> + ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
> + ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
> + ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
> + if (copy_to_user(params, &ret, sizeof(ret)))
> + return -EFAULT;
> + return 0;
> +}
> +
> +static void ext4_sb_setparams(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> +{
> + const struct ext4_tune_sb_params *params = arg;
> +
> + if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
> + es->s_errors = cpu_to_le16(params->errors_behavior);
> + if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
> + es->s_mnt_count = cpu_to_le16(params->mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
> + es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
> + es->s_checkinterval = cpu_to_le32(params->checkinterval);
> + if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
> + es->s_lastcheck = cpu_to_le32(params->last_check_time);
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
> + ext4_fsblk_t blk = params->reserved_blocks;
> +
> + es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
> + es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
> + int uid = params->reserved_uid;
> +
> + es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
> + es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
> + int gid = params->reserved_gid;
> +
> + es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
> + es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
> + es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
> + if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + es->s_def_hash_version = params->def_hash_alg;
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
> + es->s_raid_stride = cpu_to_le16(params->raid_stride);
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> + es->s_raid_stripe_width =
> + cpu_to_le32(params->raid_stripe_width);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING)
> + es->s_encoding = cpu_to_le16(params->encoding);
> + if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
> + es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
> + strscpy_pad(es->s_mount_opts, params->mount_opts);
> + if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + es->s_feature_compat |=
> + cpu_to_le32(params->set_feature_compat_mask);
> + es->s_feature_incompat |=
> + cpu_to_le32(params->set_feature_incompat_mask);
> + es->s_feature_ro_compat |=
> + cpu_to_le32(params->set_feature_ro_compat_mask);
> + es->s_feature_compat &=
> + ~cpu_to_le32(params->clear_feature_compat_mask);
> + es->s_feature_incompat &=
> + ~cpu_to_le32(params->clear_feature_incompat_mask);
> + es->s_feature_ro_compat &=
> + ~cpu_to_le32(params->clear_feature_ro_compat_mask);
> + if (params->set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)
> + es->s_def_hash_version = sbi->s_def_hash_version;
> + if (params->set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED)
> + es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
> + es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
> +}
> +
> +static int ext4_ioctl_set_tune_sb(struct file *filp,
> + struct ext4_tune_sb_params __user *in)
> +{
> + struct ext4_tune_sb_params params;
> + struct super_block *sb = file_inode(filp)->i_sb;
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct ext4_super_block *es = sbi->s_es;
> + int enabling_casefold = 0;
> + int ret;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (copy_from_user(¶ms, in, sizeof(params)))
> + return -EFAULT;
> +
> + if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
> + return -EOPNOTSUPP;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
> + (params.errors_behavior > EXT4_ERRORS_PANIC))
> + return -EINVAL;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
> + (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
> + ((params.def_hash_alg > DX_HASH_LAST) ||
> + (params.def_hash_alg == DX_HASH_SIPHASH)))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
> + (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
> + return -EINVAL;
> +
> + if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
> + params.set_feature_compat_mask =
> + params.feature_compat &
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask =
> + params.feature_incompat &
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask =
> + params.feature_ro_compat &
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + params.clear_feature_compat_mask =
> + ~params.feature_compat &
> + le32_to_cpu(es->s_feature_compat);
> + params.clear_feature_incompat_mask =
> + ~params.feature_incompat &
> + le32_to_cpu(es->s_feature_incompat);
> + params.clear_feature_ro_compat_mask =
> + ~params.feature_ro_compat &
> + le32_to_cpu(es->s_feature_ro_compat);
> + params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + if ((params.set_feature_compat_mask &
> + ~EXT4_TUNE_SET_COMPAT_SUPP) ||
> + (params.set_feature_incompat_mask &
> + ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
> + (params.set_feature_ro_compat_mask &
> + ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
> + (params.clear_feature_compat_mask &
> + ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
> + (params.clear_feature_incompat_mask &
> + ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
> + (params.clear_feature_ro_compat_mask &
> + ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
> + return -EOPNOTSUPP;
> +
> + /*
> + * Filter out the features that are already set from
> + * the set_mask.
> + */
> + params.set_feature_compat_mask &=
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask &=
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask &=
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + if ((params.set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)) {
> + enabling_casefold = 1;
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING)) {
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING;
> + }
> + if (!(params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)) {
> + params.encoding_flags = 0;
> + params.set_flags |= EXT4_TUNE_FL_ENCODING_FLAGS;
> + }
> + }
> + if ((params.set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)) {
> + uuid_t uu;
> +
> + memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
> + if (uuid_is_null(&uu))
> + generate_random_uuid((char *)
> + &sbi->s_hash_seed);
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> + else if (sbi->s_def_hash_version == 0)
> + sbi->s_def_hash_version = DX_HASH_HALF_MD4;
> + if (!(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
> + !(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
> +#ifdef __CHAR_UNSIGNED__
> + sbi->s_hash_unsigned = 3;
> +#else
> + sbi->s_hash_unsigned = 0;
> +#endif
> + }
> + }
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding == 0)
> + params.encoding = EXT4_ENC_UTF8_12_1;
> + else if (params.encoding != EXT4_ENC_UTF8_12_1)
> + return -EINVAL;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_ENCODING_FLAGS) {
> + if (!enabling_casefold)
> + return -EINVAL;
> + if (params.encoding_flags & ~SB_ENC_SUPP_MASK)
> + return -EINVAL;
> + }
> +
> + ret = mnt_want_write_file(filp);
> + if (ret)
> + return ret;
> +
> + ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
> + mnt_drop_write_file(filp);
> +
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> +
> + return ret;
> +}
> +
> static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> struct inode *inode = file_inode(filp);
> @@ -1616,6 +1908,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
> case EXT4_IOC_SETFSUUID:
> return ext4_ioctl_setuuid(filp, (const void __user *)arg);
> + case EXT4_IOC_GET_TUNE_SB_PARAM:
> + return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
> + (void __user *)arg);
> + case EXT4_IOC_SET_TUNE_SB_PARAM:
> + return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
> default:
> return -ENOTTY;
> }
> @@ -1703,7 +2000,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> }
> #endif
>
> -static void set_overhead(struct ext4_super_block *es, const void *arg)
> +static void set_overhead(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
> }
> diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
> index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..411dcc1e4a35c8c6a10f3768d17b8cc50cff4c34 100644
> --- a/include/uapi/linux/ext4.h
> +++ b/include/uapi/linux/ext4.h
> @@ -33,6 +33,8 @@
> #define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
> #define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
> #define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
> +#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
>
> #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
>
> @@ -108,6 +110,57 @@ struct ext4_new_group_input {
> __u16 unused;
> };
>
> +struct ext4_tune_sb_params {
> + __u32 set_flags;
> + __u32 checkinterval;
> + __u16 errors_behavior;
> + __u16 mnt_count;
> + __u16 max_mnt_count;
> + __u16 raid_stride;
> + __u64 last_check_time;
> + __u64 reserved_blocks;
> + __u64 blocks_count;
> + __u32 default_mnt_opts;
> + __u32 reserved_uid;
> + __u32 reserved_gid;
> + __u32 raid_stripe_width;
> + __u16 encoding;
> + __u16 encoding_flags;
> + __u8 def_hash_alg;
> + __u8 pad_1;
> + __u16 pad_2;
> + __u32 feature_compat;
> + __u32 feature_incompat;
> + __u32 feature_ro_compat;
> + __u32 set_feature_compat_mask;
> + __u32 set_feature_incompat_mask;
> + __u32 set_feature_ro_compat_mask;
> + __u32 clear_feature_compat_mask;
> + __u32 clear_feature_incompat_mask;
> + __u32 clear_feature_ro_compat_mask;
> + __u8 mount_opts[64];
> + __u8 pad[64];
> +};
> +
> +#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
> +#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
> +#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
> +#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
> +#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
> +#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
> +#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
> +#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
> +#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
> +#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
> +#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
> +#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
> +#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
> +#define EXT4_TUNE_FL_FEATURES 0x00002000
> +#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
> +#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
> +#define EXT4_TUNE_FL_ENCODING 0x00010000
> +#define EXT4_TUNE_FL_ENCODING_FLAGS 0x00020000
> +
> /*
> * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
> * It indicates that the entry in extent status cache is for a hole.
>
> --
> 2.51.0
>
>
>
^ permalink raw reply
* Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-09-18 17:56 UTC (permalink / raw)
To: Will Deacon
Cc: brauner, Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Shuah Khan, linux-kernel,
Catalin Marinas, jannh, Andrew Morton, Yury Khrustalev,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook,
Adhemerval Zanella Netto
In-Reply-To: <aMwtdtRHT7oHhYLf@willie-the-truck>
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On Thu, Sep 18, 2025 at 05:04:06PM +0100, Will Deacon wrote:
> On Thu, Sep 18, 2025 at 01:38:53PM +0100, Will Deacon wrote:
> > It would be great if Christian could give this the thumbs up, given that
> > it changes clone3(). I think the architecture parts are all ready at this
> > point.
> ah, I may have spoken too soon :/
Well, there's also the fact that this is based on the vfs tree (or would
have conflicts with it).
> Catalin pointed me at this glibc thread:
> https://marc.info/?l=glibc-alpha&m=175811917427562
> which sounds like they're not entirely on board with the new ABI.
I think we're getting there on that one, and the main thing they're
asking for is the ability to reuse the GCS after the thread has exited
which would be orthogonal to this stuff. I see Catalin replied on the
glibc side so I'll direct most of my reply there.
It would be really helpful to get a clear idea of where we're going with
this series, it's been almost landed for an incredibly long time and
having it in that state is getting disruptive to doing cleanup to try to
factor code out of the arches especially with the RISC-V stuff also up
in the air. I do think the issues glibc have with this are orthogonal
to the changes here so hopefully this can go as is.
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^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Askar Safin @ 2025-09-18 19:58 UTC (permalink / raw)
To: nschichan
Cc: akpm, andy.shevchenko, axboe, brauner, cyphar, devicetree,
ecurtin, email2tema, graf, gregkh, hca, hch, hsiangkao, initramfs,
jack, julian.stecklina, kees, linux-acpi, linux-alpha, linux-api,
linux-arch, linux-arm-kernel, linux-block, linux-csky, linux-doc,
linux-efi, linux-ext4, linux-fsdevel, linux-hexagon, linux-kernel,
linux-m68k, linux-mips, linux-openrisc, linux-parisc, linux-riscv,
linux-s390, linux-sh, linux-snps-arc, linux-um, linuxppc-dev,
loongarch, mcgrof, mingo, monstr, mzxreary, patches, rob,
safinaskar, sparclinux, thomas.weissschuh, thorsten.blum,
torvalds, tytso, viro, x86
In-Reply-To: <20250918152830.438554-1-nschichan@freebox.fr>
> When booting with root=/dev/ram0 in the kernel commandline,
> handle_initrd() where the deprecation message resides is never called,
> which is rather unfortunate (init/do_mounts_initrd.c):
Yes, this is unfortunate.
I personally still think that initrd should be removed.
I suggest using workaround I described in cover letter.
Also, for unknown reasons I didn't get your letter in my inbox.
(Not even in spam folder.) I ocasionally found it on lore.kernel.org .
--
Askar Safin
^ permalink raw reply
* [PATCH v4 00/10] man2: document "new" mount API
From: Aleksa Sarai @ 2025-09-19 1:59 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner, Aleksa Sarai
Back in 2019, the new mount API was merged[1]. David Howells then set
about writing man pages for these new APIs, and sent some patches back
in 2020[2].
Unfortunately, these patches were never merged, which meant that these
APIs were practically undocumented for many years -- arguably this has
been a contributing factor to the relatively slow adoption of these new
(far better) APIs. For instance, I have often discovered that many folks
are unaware of the read(2)-based message retrieval interface provided by
filesystem context file descriptors.
In 2024, Christian Brauner adapted David Howell's original man pages
into the easier-to-edit Markdown format and published them on GitHub[3].
These have been maintained since, including updated information on new
features added since David Howells's 2020 draft pages (such as
MOVE_MOUNT_BENEATH).
While this was a welcome improvement to the previous status quo (that
had lasted over 6 years), speaking personally my experience is that not
having access to these man pages from the terminal has been a fairly
common painpoint.
So, this is a modern version of the man pages for these APIs, in the
hopes that we can finally (6 years later) get proper documentation for
these APIs in the man-pages project.
One important thing to note is that most of these were re-written by me,
with very minimal copying from the versions available from Christian[2].
The reasons for this are two-fold:
* Both Howells's original version and Christian's maintained versions
contain crucial mistakes that I have been bitten by in the past (the
most obvious being that all of these APIs were merged in Linux 5.2,
but the man pages all claim they were merged in different versions.)
* As the man pages appear to have been written from Howells's
perspective while implementing them, some of the wording is a little
too tied to the implementation (or appears to describe features that
don't really exist in the merged versions of these APIs).
* The original versions of the man-pages lacked bigger-picture
explanations of the reasoning behind the API, which would make it
easier for readers to understand what operations are doing.
I decided that the best way to resolve these issues is to rewrite them
from the perspective of an actual user of these APIs (me), and check
that we do not repeat the mistakes I found in the originals. I have also
done my best to resolve the issues raised by Michael Kerrisk on the
original patchset sent by Howells[1].
In addition, I have also included a man page for open_tree_attr(2) (as a
subsection of the new open_tree(2) man page), which was merged in Linux
6.15.
[1]: https://lore.kernel.org/all/20190507204921.GL23075@ZenIV.linux.org.uk/
[2]: https://lore.kernel.org/linux-man/159680892602.29015.6551860260436544999.stgit@warthog.procyon.org.uk/
[3]: https://github.com/brauner/man-pages-md
Co-authored-by: David Howells <dhowells@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Co-authored-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
Changes in v4:
- `sed -i s|\\% |\\%|g`.
- Remove unneeded quotes in SYNOPSIS. [Alejandro Colomar]
- open_tree(2): fix leftover confusing usages of "attach" when referring
to file descriptors being associated with mount objects.
- open_tree(2): rename "Anonymous mount namespaces" NOTES subsection to
the far more informative "Mount propagation" and clean up the wording
a little.
- open_tree_attr(2): add a code comment about
<https://lore.kernel.org/all/20250808-open_tree_attr-bugfix-idmap-v1-0-0ec7bc05646c@cyphar.com/>
- {fsconfig,open_tree_attr}(2): use _Nullable.
- {fsmount,open_tree}(2): mention the the unmount-on-close behaviour is
actually lazy (a-la MNT_DETACH).
- {fsconfig,mount_setattr}(2): improve "mount attributes and filesystem
parameters" wording to make it clearer that superblock and mount flags
are sibling properties, not the same thing.
- open_tree(2): mention that any mount propagation events while the mount
object is detached are completely lost -- i.e., they don't get replayed once
you attach the mount somewhere.
- fsconfig(2): fix minor grammatical / missing joining word issues.
- fsconfig(2): fix final leftover `.IR A " and " B` cases.
- fsconfig(2): explain that failed fsconfig(FSCONFIG_CMD_*) operations render
the filesystem context invalid.
- fsconfig(2): rework the description of superblock reuse, as the previous text
was very wrong. (Though there has been discussion about changing this
behaviour...)
- fsconfig(2): remove misleading wording in FSCONFIG_CMD_CREATE_EXCL about how
we are requesting a new filesystem instance -- in theory filesystems could
take this request into account but in practice none do (and it seems unlikely
any ever will).
- fsconfig(2): mention that key, value, and aux must be 0 or NULL for
FSCONFIG_CMD_RECONF.
- fsmount(2): fix usage of "filesystem instance" in relation to fsmount() and
open_tree() comparison. [Askar Safin]
- move_mount(2): "as attached" -> "as a detached" [Askar Safin]
- fspick(2): add note about filesystem parameter list being copied rather than
reset with FSCONFIG_CMD_RECONFIGURE. [Askar Safin]
- v3: <https://lore.kernel.org/r/20250809-new-mount-api-v3-0-f61405c80f34@cyphar.com>
Changes in v3:
- `sed -i s|Co-developed-by|Co-authored-by|g`. [Alejandro Colomar]
- Add Signed-off-by for co-authors. [Christian Brauner]
- `sed -i s|needs-mount|awaiting-mount|g`, to match the kernel parlance.
- Fix VERSIONS/HISTORY mixup in mount_attr(2type) that was copied from
open_how(2type). [Alejandro Colomar]
- Fix incorrect .BR usage in SYNOPSIS.
- Some more semantic newlines fixes. [Alejandro Colomar]
- Minor fixes suggested by Alejandro. [Alejandro Colomar]
- open_tree_attr(2): heavily reword everything to be better formatted
and more explicit about its behaviour.
- open_tree(2): write proper explanatory paragraphs for the EXAMPLES.
- mount_setattr(2): fix stray doublequote in SYNOPSIS. [Askar Safin]
- fsopen(2): rework structure of the DESCRIPTION introduction.
- fsopen(2): explicitly say that read(2) errors in the message retrieval
interface are actual errors, not return 0. [Askar Safin]
- fsopen(2): add BUGS section to describe the unfortunate -ENODATA
message dropping behaviour that should be fixed by
<https://lore.kernel.org/r/20250807-fscontext-log-cleanups-v3-0-8d91d6242dc3@cyphar.com/>.
- fsconfig(2): add a NOTES subsection about generic filesystem
parameters.
- fsconfig(2): add comment about the weirdness surrounding
FSCONFIG_SET_PATH.
- {fspick,open_tree}(2): Correct AT_NO_AUTOMOUNT description (copied
from David, who probably copied it from statx(2)) -- AT_NO_AUTOMOUNT
applies to all path components, not just the final one. [Christian
Brauner]
- statx(2): fix AT_NO_AUTOMOUNT documentation.
- open_tree(2): swap open(2) reference for openat(2) when saying that
the result is identical. [Askar Safin]
- fsmount(2): fix DESCRIPTION introduction, and rework attr_flags
description to better reference mount_setattr(2).
- {fsopen,fspick,fsmount,open_tree}(2): don't use "attach" when talking
about the file descriptors we return that reference in-kernel objects,
to avoid confusing readers with mount object attachment status.
- fsconfig(2): remove pidns argument example, as it was kind of unclear
and referenced kernel features not yet merged.
- fsconfig(2): remove rambling FSCONFIG_SET_PATH_EMPTY text (which
mostly describes an academic issue that doesn't apply to any existing
filesystem), and instead add a CAVEATS section which touches on the
weird type behaviour of fsconfig(2).
- v2: <https://lore.kernel.org/r/20250807-new-mount-api-v2-0-558a27b8068c@cyphar.com>
Changes in v2:
- `make -R lint-man`. [Alejandro Colomar]
- `sed -i s|Glibc|glibc|g`. [Alejandro Colomar]
- `sed -i s|pathname|path|g` [Alejandro Colomar]
- Clean up macro usage, example code, and synopsis. [Alejandro Colomar]
- Try to use semantic newlines. [Alejandro Colomar]
- Make sure the usage of "filesystem context", "filesystem instance",
and "mount object" are consistent. [Askar Safin]
- Avoid referring to these syscalls without an "at" suffix as "*at()
syscalls". [Askar Safin]
- Use \% to avoid hyphenation of constants. [Askar Safin, G. Branden Robinson]
- Add a new subsection to mount_setattr(2) to describe the distinction
between mount attributes and filesystem parameters.
- (Under protest) double-space-after-period formatted commit messages.
- v1: <https://lore.kernel.org/r/20250806-new-mount-api-v1-0-8678f56c6ee0@cyphar.com>
---
Aleksa Sarai (10):
man/man2/mount_setattr.2: move mount_attr struct to mount_attr(2type)
man/man2/fsopen.2: document "new" mount API
man/man2/fspick.2: document "new" mount API
man/man2/fsconfig.2: document "new" mount API
man/man2/fsmount.2: document "new" mount API
man/man2/move_mount.2: document "new" mount API
man/man2/open_tree.2: document "new" mount API
man/man2/mount_setattr.2: mirror opening sentence from fsopen(2)
man/man2/open_tree{,_attr}.2: document new open_tree_attr() API
man/man2/{fsconfig,mount_setattr}.2: add note about attribute-parameter distinction
man/man2/fsconfig.2 | 739 ++++++++++++++++++++++++++++++++++++++++++
man/man2/fsmount.2 | 231 +++++++++++++
man/man2/fsopen.2 | 384 ++++++++++++++++++++++
man/man2/fspick.2 | 342 +++++++++++++++++++
man/man2/mount_setattr.2 | 63 +++-
man/man2/move_mount.2 | 646 ++++++++++++++++++++++++++++++++++++
man/man2/open_tree.2 | 638 ++++++++++++++++++++++++++++++++++++
man/man2/open_tree_attr.2 | 1 +
man/man2type/mount_attr.2type | 61 ++++
9 files changed, 3092 insertions(+), 13 deletions(-)
---
base-commit: e86f9fd0c279f593242969a2fbb5ef379272d89d
change-id: 20250802-new-mount-api-436db984f432
Kind regards,
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
^ permalink raw reply
* [PATCH v4 01/10] man/man2/mount_setattr.2: move mount_attr struct to mount_attr(2type)
From: Aleksa Sarai @ 2025-09-19 1:59 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner, Aleksa Sarai
In-Reply-To: <20250919-new-mount-api-v4-0-1261201ab562@cyphar.com>
As with open_how(2type), it makes sense to move this to a separate man
page. In addition, future man pages added in this patchset will want to
reference mount_attr(2type).
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
man/man2/mount_setattr.2 | 17 ++++--------
man/man2type/mount_attr.2type | 61 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 66 insertions(+), 12 deletions(-)
diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
index 586633f48e894bf8f2823aa7755c96adcddea6a6..4b55f6d2e09d00d9bc4b3a085f310b1b459f34e8 100644
--- a/man/man2/mount_setattr.2
+++ b/man/man2/mount_setattr.2
@@ -114,18 +114,11 @@ .SH DESCRIPTION
.I attr
argument of
.BR mount_setattr ()
-is a structure of the following form:
-.P
-.in +4n
-.EX
-struct mount_attr {
- __u64 attr_set; /* Mount properties to set */
- __u64 attr_clr; /* Mount properties to clear */
- __u64 propagation; /* Mount propagation type */
- __u64 userns_fd; /* User namespace file descriptor */
-};
-.EE
-.in
+is a pointer to a
+.I mount_attr
+structure,
+described in
+.BR mount_attr (2type).
.P
The
.I attr_set
diff --git a/man/man2type/mount_attr.2type b/man/man2type/mount_attr.2type
new file mode 100644
index 0000000000000000000000000000000000000000..f5c4f48be46ec1e6c0d3a211b6724a1e95311a41
--- /dev/null
+++ b/man/man2type/mount_attr.2type
@@ -0,0 +1,61 @@
+.\" Copyright, the authors of the Linux man-pages project
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH mount_attr 2type (date) "Linux man-pages (unreleased)"
+.SH NAME
+mount_attr \- what mount properties to set and clear
+.SH LIBRARY
+Linux kernel headers
+.SH SYNOPSIS
+.EX
+.B #include <sys/mount.h>
+.P
+.B struct mount_attr {
+.BR " u64 attr_set;" " /* Mount properties to set */"
+.BR " u64 attr_clr;" " /* Mount properties to clear */"
+.BR " u64 propagation;" " /* Mount propagation type */"
+.BR " u64 userns_fd;" " /* User namespace file descriptor */"
+ /* ... */
+.B };
+.EE
+.SH DESCRIPTION
+Specifies which mount properties should be changed with
+.BR mount_setattr (2).
+.P
+The fields are as follows:
+.TP
+.I .attr_set
+This field specifies which
+.BI MOUNT_ATTR_ *
+attribute flags to set.
+.TP
+.I .attr_clr
+This field specifies which
+.BI MOUNT_ATTR_ *
+attribute flags to clear.
+.TP
+.I .propagation
+This field specifies what mount propagation will be applied.
+The valid values of this field are the same propagation types described in
+.BR mount_namespaces (7).
+.TP
+.I .userns_fd
+This field specifies a file descriptor that indicates which user namespace to
+use as a reference for ID-mapped mounts with
+.BR MOUNT_ATTR_IDMAP .
+.SH STANDARDS
+Linux.
+.SH HISTORY
+Linux 5.12.
+.\" commit 2a1867219c7b27f928e2545782b86daaf9ad50bd
+glibc 2.36.
+.P
+Extra fields may be appended to the structure,
+with a zero value in a new field resulting in
+the kernel behaving as though that extension field was not present.
+Therefore, a user
+.I must
+zero-fill this structure on initialization.
+.SH SEE ALSO
+.BR mount_setattr (2)
--
2.51.0
^ permalink raw reply related
* [PATCH v4 02/10] man/man2/fsopen.2: document "new" mount API
From: Aleksa Sarai @ 2025-09-19 1:59 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner, Aleksa Sarai
In-Reply-To: <20250919-new-mount-api-v4-0-1261201ab562@cyphar.com>
This is loosely based on the original documentation written by David
Howells and later maintained by Christian Brauner, but has been
rewritten to be more from a user perspective (as well as fixing a few
critical mistakes).
Co-authored-by: David Howells <dhowells@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Co-authored-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
man/man2/fsopen.2 | 384 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 384 insertions(+)
diff --git a/man/man2/fsopen.2 b/man/man2/fsopen.2
new file mode 100644
index 0000000000000000000000000000000000000000..7cdbeac7d64b7e5c969dee619a039ec947d1e981
--- /dev/null
+++ b/man/man2/fsopen.2
@@ -0,0 +1,384 @@
+.\" Copyright, the authors of the Linux man-pages project
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH fsopen 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+fsopen \- create a new filesystem context
+.SH LIBRARY
+Standard C library
+.RI ( libc ,\~ \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <sys/mount.h>
+.P
+.BI "int fsopen(const char *" fsname ", unsigned int " flags );
+.fi
+.SH DESCRIPTION
+The
+.BR fsopen ()
+system call is part of
+the suite of file descriptor based mount facilities in Linux.
+.P
+.BR fsopen ()
+creates a blank filesystem configuration context within the kernel
+for the filesystem named by
+.I fsname
+and places it into creation mode.
+A new file descriptor
+associated with the filesystem configuration context
+is then returned.
+The calling process must have the
+.B \%CAP_SYS_ADMIN
+capability in order to create a new filesystem configuration context.
+.P
+A filesystem configuration context is
+an in-kernel representation of a pending transaction,
+containing a set of configuration parameters that are to be applied
+when creating a new instance of a filesystem
+(or modifying the configuration of an existing filesystem instance,
+such as when using
+.BR fspick (2)).
+.P
+After obtaining a filesystem configuration context with
+.BR fsopen (),
+the general workflow for operating on the context looks like the following:
+.IP (1) 5
+Pass the filesystem context file descriptor to
+.BR fsconfig (2)
+to specify any desired filesystem parameters.
+This may be done as many times as necessary.
+.IP (2)
+Pass the same filesystem context file descriptor to
+.BR fsconfig (2)
+with
+.B \%FSCONFIG_CMD_CREATE
+to create an instance of the configured filesystem.
+.IP (3)
+Pass the same filesystem context file descriptor to
+.BR fsmount (2)
+to create a new detached mount object for
+the root of the filesystem instance,
+which is then attached to a new file descriptor.
+(This also places the filesystem context file descriptor into
+reconfiguration mode,
+similar to the mode produced by
+.BR fspick (2).)
+Once a mount object has been created with
+.BR fsmount (2),
+the filesystem context file descriptor can be safely closed.
+.IP (4)
+Now that a mount object has been created,
+you may
+.RS
+.IP (4.1) 7
+use the detached mount object file descriptor as a
+.I dirfd
+argument to "*at()" system calls; and/or
+.IP (4.2) 7
+attach the mount object to a mount point
+by passing the mount object file descriptor to
+.BR move_mount (2).
+This will also prevent the mount object from
+being unmounted and destroyed when
+the mount object file descriptor is closed.
+.RE
+.IP
+The mount object file descriptor will
+remain associated with the mount object
+even after doing the above operations,
+so you may repeatedly use the mount object file descriptor with
+.BR move_mount (2)
+and/or "*at()" system calls
+as many times as necessary.
+.P
+A filesystem context will move between different modes
+throughout its lifecycle
+(such as the creation phase
+when created with
+.BR fsopen (),
+the reconfiguration phase
+when an existing filesystem instance is selected with
+.BR fspick (2),
+and the intermediate "awaiting-mount" phase
+.\" FS_CONTEXT_AWAITING_MOUNT is the term the kernel uses for this.
+between
+.BR \%FSCONFIG_CMD_CREATE
+and
+.BR fsmount (2)),
+which has an impact on
+what operations are permitted on the filesystem context.
+.P
+The file descriptor returned by
+.BR fsopen ()
+also acts as a channel for filesystem drivers to
+provide more comprehensive diagnostic information
+than is normally provided through the standard
+.BR errno (3)
+interface for system calls.
+If an error occurs at any time during the workflow mentioned above,
+calling
+.BR read (2)
+on the filesystem context file descriptor
+will retrieve any ancillary information about the encountered errors.
+(See the "Message retrieval interface" section
+for more details on the message format.)
+.P
+.I flags
+can be used to control aspects of
+the creation of the filesystem configuration context file descriptor.
+A value for
+.I flags
+is constructed by bitwise ORing
+zero or more of the following constants:
+.RS
+.TP
+.B FSOPEN_CLOEXEC
+Set the close-on-exec
+.RB ( FD_CLOEXEC )
+flag on the new file descriptor.
+See the description of the
+.B O_CLOEXEC
+flag in
+.BR open (2)
+for reasons why this may be useful.
+.RE
+.P
+A list of filesystems supported by the running kernel
+(and thus a list of valid values for
+.IR fsname )
+can be obtained from
+.IR /proc/filesystems .
+(See also
+.BR proc_filesystems (5).)
+.SS Message retrieval interface
+When doing operations on a filesystem configuration context,
+the filesystem driver may choose to provide
+ancillary information to userspace
+in the form of message strings.
+.P
+The filesystem context file descriptors returned by
+.BR fsopen ()
+and
+.BR fspick (2)
+may be queried for message strings at any time by calling
+.BR read (2)
+on the file descriptor.
+Each call to
+.BR read (2)
+will return a single message,
+prefixed to indicate its class:
+.RS
+.TP
+\fBe\fP <\fImessage\fP>
+An error message was logged.
+This is usually associated with an error being returned
+from the corresponding system call which triggered this message.
+.TP
+\fBw\fP <\fImessage\fP>
+A warning message was logged.
+.TP
+\fBi\fP <\fImessage\fP>
+An informational message was logged.
+.RE
+.P
+Messages are removed from the queue as they are read.
+Note that the message queue has limited depth,
+so it is possible for messages to get lost.
+If there are no messages in the message queue,
+.B read(2)
+will return \-1 and
+.I errno
+will be set to
+.BR \%ENODATA .
+If the
+.I buf
+argument to
+.BR read (2)
+is not large enough to contain the entire message,
+.BR read (2)
+will return \-1 and
+.I errno
+will be set to
+.BR \%EMSGSIZE .
+(See BUGS.)
+.P
+If there are multiple filesystem contexts
+referencing the same filesystem instance
+(such as if you call
+.BR fspick (2)
+multiple times for the same mount),
+each one gets its own independent message queue.
+This does not apply to multiple file descriptors that are
+tied to the same underlying open file description
+(such as those created with
+.BR dup (2)).
+.P
+Message strings will usually be prefixed by
+the name of the filesystem or kernel subsystem
+that logged the message,
+though this may not always be the case.
+See the Linux kernel source code for details.
+.SH RETURN VALUE
+On success, a new file descriptor is returned.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EFAULT
+.I fsname
+is NULL
+or a pointer to a location
+outside the calling process's accessible address space.
+.TP
+.B EINVAL
+.I flags
+had an invalid flag set.
+.TP
+.B EMFILE
+The calling process has too many open files to create more.
+.TP
+.B ENFILE
+The system has too many open files to create more.
+.TP
+.B ENODEV
+The filesystem named by
+.I fsname
+is not supported by the kernel.
+.TP
+.B ENOMEM
+The kernel could not allocate sufficient memory to complete the operation.
+.TP
+.B EPERM
+The calling process does not have the required
+.B \%CAP_SYS_ADMIN
+capability.
+.SH STANDARDS
+Linux.
+.SH HISTORY
+Linux 5.2.
+.\" commit 24dcb3d90a1f67fe08c68a004af37df059d74005
+.\" commit 400913252d09f9cfb8cce33daee43167921fc343
+glibc 2.36.
+.SH BUGS
+.SS Message retrieval interface and \fB\%EMSGSIZE\fP
+As described in the "Message retrieval interface" subsection above,
+calling
+.BR read (2)
+with too small a buffer to contain
+the next pending message in the message queue
+for the filesystem configuration context
+will cause
+.BR read (2)
+to return \-1 and set
+.BR errno (3)
+to
+.BR \%EMSGSIZE .
+.P
+However,
+this failed operation still
+consumes the message from the message queue.
+This effectively discards the message silently,
+as no data is copied into the
+.BR read (2)
+buffer.
+.P
+Programs should take care to ensure that
+their buffers are sufficiently large
+to contain any reasonable message string,
+in order to avoid silently losing valuable diagnostic information.
+.\" Aleksa Sarai
+.\" This unfortunate behaviour has existed since this feature was merged, but
+.\" I have sent a patchset which will finally fix it.
+.\" <https://lore.kernel.org/r/20250807-fscontext-log-cleanups-v3-1-8d91d6242dc3@cyphar.com/>
+.SH EXAMPLES
+To illustrate the workflow for creating a new mount,
+the following is an example of how to mount an
+.BR ext4 (5)
+filesystem stored on
+.I /dev/sdb1
+onto
+.IR /mnt .
+.P
+.in +4n
+.EX
+int fsfd, mntfd;
+\&
+fsfd = fsopen("ext4", FSOPEN_CLOEXEC);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
+fsconfig(fsfd, FSCONFIG_SET_PATH, "source", "/dev/sdb1", AT_FDCWD);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "noatime", NULL, 0);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "acl", NULL, 0);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "iversion", NULL, 0)
+fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_RELATIME);
+move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
+.EE
+.in
+.P
+First,
+an ext4 configuration context is created and attached to the file descriptor
+.IR fsfd .
+Then, a series of parameters
+(such as the source of the filesystem)
+are provided using
+.BR fsconfig (2),
+followed by the filesystem instance being created with
+.BR \%FSCONFIG_CMD_CREATE .
+.BR fsmount (2)
+is then used to create a new mount object attached to the file descriptor
+.IR mntfd ,
+which is then attached to the intended mount point using
+.BR move_mount (2).
+.P
+The above procedure is functionally equivalent to
+the following mount operation using
+.BR mount (2):
+.P
+.in +4n
+.EX
+mount("/dev/sdb1", "/mnt", "ext4", MS_RELATIME,
+ "ro,noatime,acl,user_xattr,iversion");
+.EE
+.in
+.P
+And here's an example of creating a mount object
+of an NFS server share
+and setting a Smack security module label.
+However, instead of attaching it to a mount point,
+the program uses the mount object directly
+to open a file from the NFS share.
+.P
+.in +4n
+.EX
+int fsfd, mntfd, fd;
+\&
+fsfd = fsopen("nfs", 0);
+fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "example.com/pub/linux", 0);
+fsconfig(fsfd, FSCONFIG_SET_STRING, "nfsvers", "3", 0);
+fsconfig(fsfd, FSCONFIG_SET_STRING, "rsize", "65536", 0);
+fsconfig(fsfd, FSCONFIG_SET_STRING, "wsize", "65536", 0);
+fsconfig(fsfd, FSCONFIG_SET_STRING, "smackfsdef", "foolabel", 0);
+fsconfig(fsfd, FSCONFIG_SET_FLAG, "rdma", NULL, 0);
+fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+mntfd = fsmount(fsfd, 0, MOUNT_ATTR_NODEV);
+fd = openat(mntfd, "src/linux-5.2.tar.xz", O_RDONLY);
+.EE
+.in
+.P
+Unlike the previous example,
+this operation has no trivial equivalent with
+.BR mount (2),
+as it was not previously possible to create a mount object
+that is not attached to any mount point.
+.SH SEE ALSO
+.BR fsconfig (2),
+.BR fsmount (2),
+.BR fspick (2),
+.BR mount (2),
+.BR mount_setattr (2),
+.BR move_mount (2),
+.BR open_tree (2),
+.BR mount_namespaces (7)
--
2.51.0
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