[PATCH v9 08/10] open: openat2(2) syscall

Aleksa Sarai
2019-07-06T15:00:39Z

The most obvious syscall to add support for the new LOOKUP_* scoping
flags would be openat(2). However, there are a few reasons to not do
this:

* The new LOOKUP_* flags are intended to be security features, and
openat(2) will silently ignore all unknown flags. This means that
users would need to avoid foot-gunning themselves constantly when
using this interface if it were part of openat(2).

* Resolution scoping feels like a different operation to the existing
O_* flags. And since openat(2) has limited flag space, it seems to be
quite wasteful to clutter it with 5 flags that are all
resolution-related. Arguably O_NOFOLLOW is also a resolution flag but
its entire purpose is to error out if you encounter a trailing
symlink -- not to scope resolution.

* Other systems would be able to reimplement this syscall allowing for
cross-OS standardisation rather than being hidden amongst O_* flags
which may result in it not being used by all the parties that might
want to use it (file servers, web servers, container runtimes, etc).

* It gives us the opportunity to iterate on the O_PATH interface. In
particular, the new @how->upgrade_mask field for fd re-opening is
only possible because we have a clean slate without needing to re-use
the ACC_MODE flag design nor the existing openat(2) @mode semantics.

To this end, we introduce the openat2(2) syscall. It provides all of the
features of openat(2) through the @how->flags argument, but also
also provides a new @how->resolve argument which exposes RESOLVE_* flags
that map to our new LOOKUP_* flags. It also eliminates the long-standing
ugliness of variadic-open(2) by embedding it in a struct.

In order to allow for userspace to lock down their usage of file
descriptor re-opening, openat2(2) has the ability for users to disallow
certain re-opening modes through @how->upgrade_mask. At the moment,
there is no UPGRADE_NOEXEC.

Co-developed-by: Christian Brauner <christian@brauner.io>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/arm64/include/asm/unistd.h | 2 +-
arch/arm64/include/asm/unistd32.h | 2 +
arch/ia64/kernel/syscalls/syscall.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n64.tbl | 1 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
fs/open.c | 136 ++++++++++++++------
include/linux/fcntl.h | 15 ++-
include/linux/fs.h | 4 +-
include/linux/syscalls.h | 14 +-
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/fcntl.h | 38 ++++++
24 files changed, 186 insertions(+), 46 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 9e7704e44f6d..1703d048c141 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -461,6 +461,7 @@
530 common getegid sys_getegid
531 common geteuid sys_geteuid
532 common getppid sys_getppid
+533 common openat2 sys_openat2
# all other architectures have common numbers for new syscall, alpha
# is the exception.
534 common pidfd_send_signal sys_pidfd_send_signal
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index aaf479a9e92d..4ad262698396 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -447,3 +447,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index c9f8dd421c5f..0d4aa3e5389e 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -33,7 +33,7 @@
#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)

-#define __NR_compat_syscalls 434
+#define __NR_compat_syscalls 435
#endif

#define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index aa995920bd34..b134419c0421 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -875,6 +875,8 @@ __SYSCALL(__NR_fsconfig, sys_fsconfig)
__SYSCALL(__NR_fsmount, sys_fsmount)
#define __NR_fspick 433
__SYSCALL(__NR_fspick, sys_fspick)
+#define __NR_openat2 434
+__SYSCALL(__NR_openat2, sys_openat2)

/*
* Please add new compat syscalls above this comment and update
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index e01df3f2f80d..28d954acf214 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -354,3 +354,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 7e3d0734b2f3..b744b1a1c80e 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -433,3 +433,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 26339e417695..bee07b73a898 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -439,3 +439,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 0e2dd68ade57..a3ec5e27630a 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -372,3 +372,4 @@
431 n32 fsconfig sys_fsconfig
432 n32 fsmount sys_fsmount
433 n32 fspick sys_fspick
+434 n32 openat2 sys_openat2
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 5eebfa0d155c..3503ac6ef482 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -348,3 +348,4 @@
431 n64 fsconfig sys_fsconfig
432 n64 fsmount sys_fsmount
433 n64 fspick sys_fspick
+434 n64 openat2 sys_openat2
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 3cc1374e02d0..e901367371c4 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -421,3 +421,4 @@
431 o32 fsconfig sys_fsconfig
432 o32 fsmount sys_fsmount
433 o32 fspick sys_fspick
+434 o32 openat2 sys_openat2 sys_openat2
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index c9e377d59232..5758b0826e4d 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -430,3 +430,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 103655d84b4b..9e8377d5b2f6 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -515,3 +515,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index e822b2964a83..d6e8eaa20d44 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -436,3 +436,4 @@
431 common fsconfig sys_fsconfig sys_fsconfig
432 common fsmount sys_fsmount sys_fsmount
433 common fspick sys_fspick sys_fspick
+434 common openat2 sys_openat2 sys_openat2
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 016a727d4357..dc38733d264b 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -436,3 +436,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index e047480b1605..cfeb24ac5299 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -479,3 +479,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ad968b7bac72..1d76a0e84f42 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -438,3 +438,4 @@
431 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig
432 i386 fsmount sys_fsmount __ia32_sys_fsmount
433 i386 fspick sys_fspick __ia32_sys_fspick
+434 i386 openat2 sys_openat2 __ia32_sys_openat2
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index b4e6f9e6204a..828bade2e505 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -355,6 +355,7 @@
431 common fsconfig __x64_sys_fsconfig
432 common fsmount __x64_sys_fsmount
433 common fspick __x64_sys_fspick
+434 common openat2 __x64_sys_openat2

#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 5fa0ee1c8e00..78ed6e97d3ae 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -404,3 +404,4 @@
431 common fsconfig sys_fsconfig
432 common fsmount sys_fsmount
433 common fspick sys_fspick
+434 common openat2 sys_openat2
diff --git a/fs/open.c b/fs/open.c
index bdca45528524..63278294d1d4 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -928,24 +928,32 @@ struct file *open_with_fake_path(const struct path *path, int flags,
}
EXPORT_SYMBOL(open_with_fake_path);

-static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
+static inline int build_open_flags(struct open_how how, struct open_flags *op)
{
int lookup_flags = 0;
- int acc_mode = ACC_MODE(flags);
+ int opath_mask = 0;
+ int acc_mode = ACC_MODE(how.flags);
+
+ if (how.resolve & ~VALID_RESOLVE_FLAGS)
+ return -EINVAL;
+ if (!(how.flags & (O_PATH | O_CREAT | __O_TMPFILE)) && how.mode != 0)
+ return -EINVAL;
+ if (memchr_inv(how.reserved, 0, sizeof(how.reserved)))
+ return -EINVAL;

/*
* Clear out all open flags we don't know about so that we don't report
* them in fcntl(F_GETFD) or similar interfaces.
*/
- flags &= VALID_OPEN_FLAGS;
+ how.flags &= VALID_OPEN_FLAGS;

- if (flags & (O_CREAT | __O_TMPFILE))
- op->mode = (mode & S_IALLUGO) | S_IFREG;
+ if (how.flags & (O_CREAT | __O_TMPFILE))
+ op->mode = (how.mode & S_IALLUGO) | S_IFREG;
else
op->mode = 0;

/* Must never be set by userspace */
- flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC;
+ how.flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC;

/*
* O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only
@@ -953,51 +961,70 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
* always set instead of having to deal with possibly weird behaviour
* for malicious applications setting only __O_SYNC.
*/
- if (flags & __O_SYNC)
- flags |= O_DSYNC;
+ if (how.flags & __O_SYNC)
+ how.flags |= O_DSYNC;

- if (flags & __O_TMPFILE) {
- if ((flags & O_TMPFILE_MASK) != O_TMPFILE)
+ if (how.flags & __O_TMPFILE) {
+ if ((how.flags & O_TMPFILE_MASK) != O_TMPFILE)
return -EINVAL;
if (!(acc_mode & MAY_WRITE))
return -EINVAL;
- } else if (flags & O_PATH) {
+ } else if (how.flags & O_PATH) {
/*
* If we have O_PATH in the open flag. Then we
* cannot have anything other than the below set of flags
*/
- flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
+ how.flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
acc_mode = 0;
+
+ /* Allow userspace to restrict the re-opening of O_PATH fds. */
+ if (how.upgrade_mask & ~VALID_UPGRADE_FLAGS)
+ return -EINVAL;
+ if (!(how.upgrade_mask & UPGRADE_NOREAD))
+ opath_mask |= FMODE_PATH_READ;
+ if (!(how.upgrade_mask & UPGRADE_NOWRITE))
+ opath_mask |= FMODE_PATH_WRITE;
}

- op->open_flag = flags;
+ op->open_flag = how.flags;

/* O_TRUNC implies we need access checks for write permissions */
- if (flags & O_TRUNC)
+ if (how.flags & O_TRUNC)
acc_mode |= MAY_WRITE;

/* Allow the LSM permission hook to distinguish append
access from general write access. */
- if (flags & O_APPEND)
+ if (how.flags & O_APPEND)
acc_mode |= MAY_APPEND;

op->acc_mode = acc_mode;
- op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
- /* For O_PATH backwards-compatibility we default to an all-set mask. */
- op->opath_mask = FMODE_PATH_READ | FMODE_PATH_WRITE;
+ op->intent = how.flags & O_PATH ? 0 : LOOKUP_OPEN;
+ op->opath_mask = opath_mask;

- if (flags & O_CREAT) {
+ if (how.flags & O_CREAT) {
op->intent |= LOOKUP_CREATE;
- if (flags & O_EXCL)
+ if (how.flags & O_EXCL)
op->intent |= LOOKUP_EXCL;
}

- if (flags & O_DIRECTORY)
+ if (how.flags & O_DIRECTORY)
lookup_flags |= LOOKUP_DIRECTORY;
- if (!(flags & O_NOFOLLOW))
+ if (!(how.flags & O_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
- if (flags & O_EMPTYPATH)
+ if (how.flags & O_EMPTYPATH)
lookup_flags |= LOOKUP_EMPTY;
+
+ if (how.resolve & RESOLVE_NO_XDEV)
+ lookup_flags |= LOOKUP_XDEV;
+ if (how.resolve & RESOLVE_NO_MAGICLINKS)
+ lookup_flags |= LOOKUP_NO_MAGICLINKS;
+ if (how.resolve & RESOLVE_NO_SYMLINKS)
+ lookup_flags |= LOOKUP_NO_SYMLINKS;
+ if (how.resolve & RESOLVE_BENEATH)
+ lookup_flags |= LOOKUP_BENEATH;
+ if (how.resolve & RESOLVE_IN_ROOT)
+ lookup_flags |= LOOKUP_IN_ROOT;
+
op->lookup_flags = lookup_flags;
return 0;
}
@@ -1016,8 +1043,14 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
struct file *file_open_name(struct filename *name, int flags, umode_t mode)
{
struct open_flags op;
- int err = build_open_flags(flags, mode, &op);
- return err ? ERR_PTR(err) : do_filp_open(AT_FDCWD, name, &op);
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+ int err = build_open_flags(how, &op);
+ if (err)
+ return ERR_PTR(err);
+ return do_filp_open(AT_FDCWD, name, &op);
}

/**
@@ -1048,17 +1081,22 @@ struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
const char *filename, int flags, umode_t mode)
{
struct open_flags op;
- int err = build_open_flags(flags, mode, &op);
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+ int err = build_open_flags(how, &op);
if (err)
return ERR_PTR(err);
return do_file_open_root(dentry, mnt, filename, &op);
}
EXPORT_SYMBOL(file_open_root);

-long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
+long do_sys_open(int dfd, const char __user *filename,
+ struct open_how *how)
{
struct open_flags op;
- int fd = build_open_flags(flags, mode, &op);
+ int fd = build_open_flags(*how, &op);
int empty = 0;
struct filename *tmp;

@@ -1071,7 +1109,7 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
if (!empty)
op.open_flag &= ~O_EMPTYPATH;

- fd = get_unused_fd_flags(flags);
+ fd = get_unused_fd_flags(how->flags);
if (fd >= 0) {
struct file *f = do_filp_open(dfd, tmp, &op);
if (IS_ERR(f)) {
@@ -1088,19 +1126,35 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)

SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
- if (force_o_largefile())
- flags |= O_LARGEFILE;
-
- return do_sys_open(AT_FDCWD, filename, flags, mode);
+ return ksys_open(filename, flags, mode);
}

SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
umode_t, mode)
{
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+
+ if (force_o_largefile())
+ how.flags |= O_LARGEFILE;
+
+ return do_sys_open(dfd, filename, &how);
+}
+
+SYSCALL_DEFINE3(openat2, int, dfd, const char __user *, filename,
+ const struct open_how __user *, how)
+{
+ struct open_how tmp;
+
+ if (copy_from_user(&tmp, how, sizeof(tmp)))
+ return -EFAULT;
+
if (force_o_largefile())
- flags |= O_LARGEFILE;
+ tmp.flags |= O_LARGEFILE;

- return do_sys_open(dfd, filename, flags, mode);
+ return do_sys_open(dfd, filename, &tmp);
}

#ifdef CONFIG_COMPAT
@@ -1110,7 +1164,11 @@ SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
*/
COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
- return do_sys_open(AT_FDCWD, filename, flags, mode);
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+ return do_sys_open(AT_FDCWD, filename, &how);
}

/*
@@ -1119,7 +1177,11 @@ COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t,
*/
COMPAT_SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, umode_t, mode)
{
- return do_sys_open(dfd, filename, flags, mode);
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+ return do_sys_open(dfd, filename, &how);
}
#endif

diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index 2868ae6c8fc1..e59917292213 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -4,13 +4,26 @@

#include <uapi/linux/fcntl.h>

-/* list of all valid flags for the open/openat flags argument: */
+/* Should open_how.mode be set for older syscalls wrappers? */
+#define OPENHOW_MODE(flags, mode) \
+ (((flags) | (O_CREAT | __O_TMPFILE)) ? (mode) : 0)
+
+/* List of all valid flags for the open/openat flags argument: */
#define VALID_OPEN_FLAGS \
(O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \
O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \
FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \
O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_EMPTYPATH)

+/* List of all valid flags for the how->upgrade_mask argument: */
+#define VALID_UPGRADE_FLAGS \
+ (UPGRADE_NOWRITE | UPGRADE_NOREAD)
+
+/* List of all valid flags for the how->resolve argument: */
+#define VALID_RESOLVE_FLAGS \
+ (RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \
+ RESOLVE_BENEATH | RESOLVE_IN_ROOT)
+
#ifndef force_o_largefile
#define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T))
#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f7df213405ea..a3aede2b3a91 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2515,8 +2515,8 @@ extern int do_truncate(struct dentry *, loff_t start, unsigned int time_attrs,
struct file *filp);
extern int vfs_fallocate(struct file *file, int mode, loff_t offset,
loff_t len);
-extern long do_sys_open(int dfd, const char __user *filename, int flags,
- umode_t mode);
+extern long do_sys_open(int dfd, const char __user *filename,
+ struct open_how *how);
extern struct file *file_open_name(struct filename *, int, umode_t);
extern struct file *filp_open(const char *, int, umode_t);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 2bcef4c70183..227303532bb7 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1369,15 +1369,21 @@ static inline int ksys_close(unsigned int fd)
return __close_fd(current->files, fd);
}

-extern long do_sys_open(int dfd, const char __user *filename, int flags,
- umode_t mode);
+extern long do_sys_open(int dfd, const char __user *filename,
+ struct open_how *how);

static inline long ksys_open(const char __user *filename, int flags,
umode_t mode)
{
+ struct open_how how = {
+ .flags = flags,
+ .mode = OPENHOW_MODE(flags, mode),
+ };
+
if (force_o_largefile())
- flags |= O_LARGEFILE;
- return do_sys_open(AT_FDCWD, filename, flags, mode);
+ how.flags |= O_LARGEFILE;
+
+ return do_sys_open(AT_FDCWD, filename, &how);
}

extern long do_sys_truncate(const char __user *pathname, loff_t length);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index a87904daf103..67486188918b 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -845,8 +845,11 @@ __SYSCALL(__NR_fsmount, sys_fsmount)
#define __NR_fspick 433
__SYSCALL(__NR_fspick, sys_fspick)

+#define __NR_openat2 435
+__SYSCALL(__NR_openat2, sys_openat2)
+
#undef __NR_syscalls
-#define __NR_syscalls 434
+#define __NR_syscalls 435

/*
* 32 bit systems traditionally used different
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 1d338357df8a..b7c904f0fca9 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -93,5 +93,43 @@

#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */

+/**
+ * Arguments for how openat2(2) should open the target path. If @extra is zero,
+ * then openat2(2) is identical to openat(2).
+ *
+ * @flags: O_* flags (unknown flags ignored).
+ * @mode: O_CREAT file mode (ignored otherwise).
+ * @upgrade_mask: restrict how the O_PATH may be re-opened (ignored otherwise).
+ * @resolve: RESOLVE_* flags (-EINVAL on unknown flags).
+ * @reserved: reserved for future extensions, must be zeroed.
+ */
+struct open_how {
+ __u32 flags;
+ union {
+ __u16 mode;
+ __u16 upgrade_mask;
+ };
+ __u16 resolve;
+ __u64 reserved[7]; /* must be zeroed */
+};
+
+/* how->resolve flags for openat2(2). */
+#define RESOLVE_NO_XDEV 0x01 /* Block mount-point crossings
+ (includes bind-mounts). */
+#define RESOLVE_NO_MAGICLINKS 0x02 /* Block traversal through procfs-style
+ "magic-links". */
+#define RESOLVE_NO_SYMLINKS 0x04 /* Block traversal through all symlinks
+ (implies OEXT_NO_MAGICLINKS) */
+#define RESOLVE_BENEATH 0x08 /* Block "lexical" trickery like
+ "..", symlinks, and absolute
+ paths which escape the dirfd. */
+#define RESOLVE_IN_ROOT 0x10 /* Make all jumps to "/" and ".."
+ be scoped inside the dirfd
+ (similar to chroot(2)). */
+
+/* how->upgrade flags for openat2(2). */
+/* First bit is reserved for a future UPGRADE_NOEXEC flag. */
+#define UPGRADE_NOREAD 0x02 /* Block re-opening with MAY_READ. */
+#define UPGRADE_NOWRITE 0x04 /* Block re-opening with MAY_WRITE. */

#endif /* _UAPI_LINUX_FCNTL_H */
--
2.22.0