[PATCH v2 0/5] Fix Kselftest's vfork() side effects

[PATCH v2 0/5] Fix Kselftest's vfork() side effects

[Mickaël Salaün]

Hi,

As reported by Kernel Test Robot [1], some pidfd tests fail.  This is
due to the use of vfork() which introduced some side effects.
Similarly, while making it more generic, a previous commit made some
Landlock file system tests flaky, and subject to the host's file system
mount configuration.

This series fixes all these side effects by replacing vfork() with
clone3() and CLONE_VFORK, which is cleaner (no arbitrary shared memory)
and makes the Kselftest framework more robust.

I tried different approaches and I found this one to be the cleaner and
less invasive for current test cases.

This second series split the latest patch into 5 patches.

I successfully ran the following tests (using TEST_F and
fork/clone/clone3) with this series:
- landlock:fs_test
- landlock:net_test
- landlock:ptrace_test
- move_mount_set_group:move_mount_set_group_test
- net/af_unix:scm_pidfd
- perf_events:remove_on_exec
- pidfd:pidfd_getfd_test
- pidfd:pidfd_setns_test
- seccomp:seccomp_bpf
- user_events:abi_test

[1] https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@intel.com

Previous version:
v1: https://lore.kernel.org/r/20240426172252.1862930-1-mic@digikod.net

Regards,

Mickaël Salaün (9):
  selftests/pidfd: Fix config for pidfd_setns_test
  selftests/landlock: Fix FS tests when run on a private mount point
  selftests/harness: Fix fixture teardown
  selftests/harness: Fix interleaved scheduling leading to race
    conditions
  selftests/landlock: Do not allocate memory in fixture data
  selftests/harness: Constify fixture variants
  selftests/pidfd: Fix wrong expectation
  selftests/harness: Share _metadata between forked processes
  selftests/harness: Fix vfork() side effects

 tools/testing/selftests/kselftest_harness.h   | 113 +++++++++++++-----
 tools/testing/selftests/landlock/fs_test.c    |  83 ++++++++-----
 tools/testing/selftests/pidfd/config          |   2 +
 .../selftests/pidfd/pidfd_setns_test.c        |   2 +-
 4 files changed, 135 insertions(+), 65 deletions(-)


base-commit: e67572cd2204894179d89bd7b984072f19313b03
-- 
2.44.0

[PATCH v2 1/9] selftests/pidfd: Fix config for pidfd_setns_test

[Mickaël Salaün]

Required by switch_timens() to open /proc/self/ns/time_for_children.

CONFIG_GENERIC_VDSO_TIME_NS is not available on UML, so pidfd_setns_test
cannot be run successfully on this architecture.

Cc: Christian Brauner <brauner@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Fixes: 2b40c5db73e2 ("selftests/pidfd: add pidfd setns tests")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-2-mic@digikod.net
---
 tools/testing/selftests/pidfd/config | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/pidfd/config b/tools/testing/selftests/pidfd/config
index f6f2965e17af..6133524710f7 100644
--- a/tools/testing/selftests/pidfd/config
+++ b/tools/testing/selftests/pidfd/config
@@ -3,5 +3,7 @@ CONFIG_IPC_NS=y
 CONFIG_USER_NS=y
 CONFIG_PID_NS=y
 CONFIG_NET_NS=y
+CONFIG_TIME_NS=y
+CONFIG_GENERIC_VDSO_TIME_NS=y
 CONFIG_CGROUPS=y
 CONFIG_CHECKPOINT_RESTORE=y
-- 
2.44.0

[PATCH v2 2/9] selftests/landlock: Fix FS tests when run on a private mount point

[Mickaël Salaün]

According to the test environment, the mount point of the test's working
directory may be shared or not, which changes the visibility of the
nested "tmp" mount point for the test's parent process calling
umount("tmp").

This was spotted while running tests in containers [1], where mount
points are private.

Cc: Günther Noack <gnoack@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Link: https://github.com/landlock-lsm/landlock-test-tools/pull/4 [1]
Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-3-mic@digikod.net
---

Changes since v1:
* Update commit description.
---
 tools/testing/selftests/landlock/fs_test.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 9a6036fbf289..46b9effd53e4 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -293,7 +293,15 @@ static void prepare_layout(struct __test_metadata *const _metadata)
 static void cleanup_layout(struct __test_metadata *const _metadata)
 {
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	EXPECT_EQ(0, umount(TMP_DIR));
+	if (umount(TMP_DIR)) {
+		/*
+		 * According to the test environment, the mount point of the
+		 * current directory may be shared or not, which changes the
+		 * visibility of the nested TMP_DIR mount point for the test's
+		 * parent process doing this cleanup.
+		 */
+		ASSERT_EQ(EINVAL, errno);
+	}
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 	EXPECT_EQ(0, remove_path(TMP_DIR));
 }
-- 
2.44.0

[PATCH v2 3/9] selftests/harness: Fix fixture teardown

[Mickaël Salaün]

Make sure fixture teardowns are run when test cases failed, including
when _metadata->teardown_parent is set to true.

Make sure only one fixture teardown is run per test case, handling the
case where the test child forks.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Shengyu Li <shengyu.li.evgeny@gmail.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Fixes: 72d7cb5c190b ("selftests/harness: Prevent infinite loop due to Assert in FIXTURE_TEARDOWN")
Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-4-mic@digikod.net
---
 tools/testing/selftests/kselftest_harness.h | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index d98702b6955d..55699a762c45 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -382,7 +382,10 @@
 		FIXTURE_DATA(fixture_name) self; \
 		pid_t child = 1; \
 		int status = 0; \
-		bool jmp = false; \
+		/* Makes sure there is only one teardown, even when child forks again. */ \
+		bool *teardown = mmap(NULL, sizeof(*teardown), \
+			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+		*teardown = false; \
 		memset(&self, 0, sizeof(FIXTURE_DATA(fixture_name))); \
 		if (setjmp(_metadata->env) == 0) { \
 			/* Use the same _metadata. */ \
@@ -399,15 +402,16 @@
 				_metadata->exit_code = KSFT_FAIL; \
 			} \
 		} \
-		else \
-			jmp = true; \
 		if (child == 0) { \
-			if (_metadata->setup_completed && !_metadata->teardown_parent && !jmp) \
+			if (_metadata->setup_completed && !_metadata->teardown_parent && \
+					__sync_bool_compare_and_swap(teardown, false, true)) \
 				fixture_name##_teardown(_metadata, &self, variant->data); \
 			_exit(0); \
 		} \
-		if (_metadata->setup_completed && _metadata->teardown_parent) \
+		if (_metadata->setup_completed && _metadata->teardown_parent && \
+				__sync_bool_compare_and_swap(teardown, false, true)) \
 			fixture_name##_teardown(_metadata, &self, variant->data); \
+		munmap(teardown, sizeof(*teardown)); \
 		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
 			/* Forward signal to __wait_for_test(). */ \
 			kill(getpid(), WTERMSIG(status)); \
-- 
2.44.0

[PATCH v2 4/9] selftests/harness: Fix interleaved scheduling leading to race conditions

[Mickaël Salaün]

Fix a race condition when running several FIXTURE_TEARDOWN() managing
the same resource.  This fixes a race condition in the Landlock file
system tests when creating or unmounting the same directory.

Using clone3() with CLONE_VFORK guarantees that the child and grandchild
test processes are sequentially scheduled.  This is implemented with a
new clone3_vfork() helper replacing the fork() call.

This avoids triggering this error in __wait_for_test():
  Test ended in some other way [127]

Cc: Christian Brauner <brauner@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Günther Noack <gnoack@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-5-mic@digikod.net
---
 tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 55699a762c45..9f04638707ae 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -66,6 +66,8 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <setjmp.h>
+#include <syscall.h>
+#include <linux/sched.h>
 
 #include "kselftest.h"
 
@@ -80,6 +82,17 @@
 #  define TH_LOG_ENABLED 1
 #endif
 
+/* Wait for the child process to end but without sharing memory mapping. */
+static pid_t __attribute__((__unused__)) clone3_vfork(void)
+{
+	struct clone_args args = {
+		.flags = CLONE_VFORK,
+		.exit_signal = SIGCHLD,
+	};
+
+	return syscall(__NR_clone3, &args, sizeof(args));
+}
+
 /**
  * TH_LOG()
  *
@@ -1183,7 +1196,7 @@ void __run_test(struct __fixture_metadata *f,
 	fflush(stdout);
 	fflush(stderr);
 
-	t->pid = fork();
+	t->pid = clone3_vfork();
 	if (t->pid < 0) {
 		ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
 		t->exit_code = KSFT_FAIL;
-- 
2.44.0

Re: [PATCH v2 4/9] selftests/harness: Fix interleaved scheduling leading to race conditions

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:26PM +0200, Mickaël Salaün wrote:
> Fix a race condition when running several FIXTURE_TEARDOWN() managing
> the same resource.  This fixes a race condition in the Landlock file
> system tests when creating or unmounting the same directory.
> 
> Using clone3() with CLONE_VFORK guarantees that the child and grandchild
> test processes are sequentially scheduled.  This is implemented with a
> new clone3_vfork() helper replacing the fork() call.
> 
> This avoids triggering this error in __wait_for_test():
>   Test ended in some other way [127]
> 
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Günther Noack <gnoack@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Will Drewry <wad@chromium.org>
> Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Link: https://lore.kernel.org/r/20240429130931.2394118-5-mic@digikod.net
> ---
>  tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
> index 55699a762c45..9f04638707ae 100644
> --- a/tools/testing/selftests/kselftest_harness.h
> +++ b/tools/testing/selftests/kselftest_harness.h
> @@ -66,6 +66,8 @@
>  #include <sys/wait.h>
>  #include <unistd.h>
>  #include <setjmp.h>
> +#include <syscall.h>
> +#include <linux/sched.h>
>  
>  #include "kselftest.h"
>  
> @@ -80,6 +82,17 @@
>  #  define TH_LOG_ENABLED 1
>  #endif
>  
> +/* Wait for the child process to end but without sharing memory mapping. */
> +static pid_t __attribute__((__unused__)) clone3_vfork(void)

Why "unused"?

> +{
> +	struct clone_args args = {
> +		.flags = CLONE_VFORK,
> +		.exit_signal = SIGCHLD,
> +	};
> +
> +	return syscall(__NR_clone3, &args, sizeof(args));
> +}
> +
>  /**
>   * TH_LOG()
>   *
> @@ -1183,7 +1196,7 @@ void __run_test(struct __fixture_metadata *f,
>  	fflush(stdout);
>  	fflush(stderr);
>  
> -	t->pid = fork();
> +	t->pid = clone3_vfork();
>  	if (t->pid < 0) {
>  		ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
>  		t->exit_code = KSFT_FAIL;

Regardless, yup, looks good.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH v2 4/9] selftests/harness: Fix interleaved scheduling leading to race conditions

[Jakub Kicinski]

On Mon, 29 Apr 2024 08:52:36 -0700 Kees Cook wrote:
> > +/* Wait for the child process to end but without sharing memory mapping. */
> > +static pid_t __attribute__((__unused__)) clone3_vfork(void)  
> 
> Why "unused"?

Right, static inline is enough

Re: [PATCH v2 4/9] selftests/harness: Fix interleaved scheduling leading to race conditions

[Mickaël Salaün]

On Mon, Apr 29, 2024 at 10:16:47AM -0700, Jakub Kicinski wrote:
> On Mon, 29 Apr 2024 08:52:36 -0700 Kees Cook wrote:
> > > +/* Wait for the child process to end but without sharing memory mapping. */
> > > +static pid_t __attribute__((__unused__)) clone3_vfork(void)  
> > 
> > Why "unused"?
> 
> Right, static inline is enough

Indeed, I'll fix that.

[PATCH v2 5/9] selftests/landlock: Do not allocate memory in fixture data

[Mickaël Salaün]

Do not allocate self->dir_path in the test process because this would
not be visible in the FIXTURE_TEARDOWN() process when relying on
fork()/clone3() instead of vfork().

This change is required for a following commit removing vfork() call to
not break the layout3_fs.* test cases.

Cc: Günther Noack <gnoack@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-6-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/landlock/fs_test.c | 57 +++++++++++++---------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 46b9effd53e4..1e2cffde02b5 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -9,6 +9,7 @@
 
 #define _GNU_SOURCE
 #include <fcntl.h>
+#include <libgen.h>
 #include <linux/landlock.h>
 #include <linux/magic.h>
 #include <sched.h>
@@ -4624,7 +4625,6 @@ FIXTURE(layout3_fs)
 {
 	bool has_created_dir;
 	bool has_created_file;
-	char *dir_path;
 	bool skip_test;
 };
 
@@ -4683,11 +4683,24 @@ FIXTURE_VARIANT_ADD(layout3_fs, hostfs) {
 	.cwd_fs_magic = HOSTFS_SUPER_MAGIC,
 };
 
+static char *dirname_alloc(const char *path)
+{
+	char *dup;
+
+	if (!path)
+		return NULL;
+
+	dup = strdup(path);
+	if (!dup)
+		return NULL;
+
+	return dirname(dup);
+}
+
 FIXTURE_SETUP(layout3_fs)
 {
 	struct stat statbuf;
-	const char *slash;
-	size_t dir_len;
+	char *dir_path = dirname_alloc(variant->file_path);
 
 	if (!supports_filesystem(variant->mnt.type) ||
 	    !cwd_matches_fs(variant->cwd_fs_magic)) {
@@ -4697,25 +4710,15 @@ FIXTURE_SETUP(layout3_fs)
 
 	_metadata->teardown_parent = true;
 
-	slash = strrchr(variant->file_path, '/');
-	ASSERT_NE(slash, NULL);
-	dir_len = (size_t)slash - (size_t)variant->file_path;
-	ASSERT_LT(0, dir_len);
-	self->dir_path = malloc(dir_len + 1);
-	self->dir_path[dir_len] = '\0';
-	strncpy(self->dir_path, variant->file_path, dir_len);
-
 	prepare_layout_opt(_metadata, &variant->mnt);
 
 	/* Creates directory when required. */
-	if (stat(self->dir_path, &statbuf)) {
+	if (stat(dir_path, &statbuf)) {
 		set_cap(_metadata, CAP_DAC_OVERRIDE);
-		EXPECT_EQ(0, mkdir(self->dir_path, 0700))
+		EXPECT_EQ(0, mkdir(dir_path, 0700))
 		{
 			TH_LOG("Failed to create directory \"%s\": %s",
-			       self->dir_path, strerror(errno));
-			free(self->dir_path);
-			self->dir_path = NULL;
+			       dir_path, strerror(errno));
 		}
 		self->has_created_dir = true;
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
@@ -4736,6 +4739,8 @@ FIXTURE_SETUP(layout3_fs)
 		self->has_created_file = true;
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
 	}
+
+	free(dir_path);
 }
 
 FIXTURE_TEARDOWN(layout3_fs)
@@ -4754,16 +4759,17 @@ FIXTURE_TEARDOWN(layout3_fs)
 	}
 
 	if (self->has_created_dir) {
+		char *dir_path = dirname_alloc(variant->file_path);
+
 		set_cap(_metadata, CAP_DAC_OVERRIDE);
 		/*
 		 * Don't check for error because the directory might already
 		 * have been removed (cf. release_inode test).
 		 */
-		rmdir(self->dir_path);
+		rmdir(dir_path);
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+		free(dir_path);
 	}
-	free(self->dir_path);
-	self->dir_path = NULL;
 
 	cleanup_layout(_metadata);
 }
@@ -4830,7 +4836,10 @@ TEST_F_FORK(layout3_fs, tag_inode_dir_mnt)
 
 TEST_F_FORK(layout3_fs, tag_inode_dir_child)
 {
-	layer3_fs_tag_inode(_metadata, self, variant, self->dir_path);
+	char *dir_path = dirname_alloc(variant->file_path);
+
+	layer3_fs_tag_inode(_metadata, self, variant, dir_path);
+	free(dir_path);
 }
 
 TEST_F_FORK(layout3_fs, tag_inode_file)
@@ -4857,9 +4866,13 @@ TEST_F_FORK(layout3_fs, release_inodes)
 	if (self->has_created_file)
 		EXPECT_EQ(0, remove_path(variant->file_path));
 
-	if (self->has_created_dir)
+	if (self->has_created_dir) {
+		char *dir_path = dirname_alloc(variant->file_path);
+
 		/* Don't check for error because of cgroup specificities. */
-		remove_path(self->dir_path);
+		remove_path(dir_path);
+		free(dir_path);
+	}
 
 	ruleset_fd =
 		create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_DIR, layer1);
-- 
2.44.0

Re: [PATCH v2 5/9] selftests/landlock: Do not allocate memory in fixture data

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:27PM +0200, Mickaël Salaün wrote:
> Do not allocate self->dir_path in the test process because this would
> not be visible in the FIXTURE_TEARDOWN() process when relying on
> fork()/clone3() instead of vfork().
> 
> This change is required for a following commit removing vfork() call to
> not break the layout3_fs.* test cases.
> 
> Cc: Günther Noack <gnoack@google.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH v2 6/9] selftests/harness: Constify fixture variants

[Mickaël Salaün]

FIXTURE_VARIANT_ADD() types are passed as const pointers to
FIXTURE_TEARDOWN().  Make that explicit by constifying the variants
declarations.

Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-7-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/kselftest_harness.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 9f04638707ae..8a7d899a75e0 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -338,7 +338,7 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
  * variant.
  */
 #define FIXTURE_VARIANT_ADD(fixture_name, variant_name) \
-	extern FIXTURE_VARIANT(fixture_name) \
+	extern const FIXTURE_VARIANT(fixture_name) \
 		_##fixture_name##_##variant_name##_variant; \
 	static struct __fixture_variant_metadata \
 		_##fixture_name##_##variant_name##_object = \
@@ -350,7 +350,7 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
 		__register_fixture_variant(&_##fixture_name##_fixture_object, \
 			&_##fixture_name##_##variant_name##_object);	\
 	} \
-	FIXTURE_VARIANT(fixture_name) \
+	const FIXTURE_VARIANT(fixture_name) \
 		_##fixture_name##_##variant_name##_variant =
 
 /**
-- 
2.44.0

Re: [PATCH v2 6/9] selftests/harness: Constify fixture variants

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:28PM +0200, Mickaël Salaün wrote:
> FIXTURE_VARIANT_ADD() types are passed as const pointers to
> FIXTURE_TEARDOWN().  Make that explicit by constifying the variants
> declarations.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Cc: Will Drewry <wad@chromium.org>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH v2 7/9] selftests/pidfd: Fix wrong expectation

[Mickaël Salaün]

Replace a wrong EXPECT_GT(self->child_pid_exited, 0) with EXPECT_GE(),
which will be actually tested on the parent and child sides with a
following commit.

Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-8-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/pidfd/pidfd_setns_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
index 6e2f2cd400ca..47746b0c6acd 100644
--- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -158,7 +158,7 @@ FIXTURE_SETUP(current_nsset)
 	/* Create task that exits right away. */
 	self->child_pid_exited = create_child(&self->child_pidfd_exited,
 					      CLONE_NEWUSER | CLONE_NEWNET);
-	EXPECT_GT(self->child_pid_exited, 0);
+	EXPECT_GE(self->child_pid_exited, 0);
 
 	if (self->child_pid_exited == 0)
 		_exit(EXIT_SUCCESS);
-- 
2.44.0

Re: [PATCH v2 7/9] selftests/pidfd: Fix wrong expectation

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:29PM +0200, Mickaël Salaün wrote:
> Replace a wrong EXPECT_GT(self->child_pid_exited, 0) with EXPECT_GE(),
> which will be actually tested on the parent and child sides with a
> following commit.
> 
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

I had to take a closer look at this one -- but yes, this should be just
checking for failure (negative). The parent/child separation is
afterwards.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH v2 8/9] selftests/harness: Share _metadata between forked processes

[Mickaël Salaün]

Unconditionally share _metadata between all forked processes, which
enables to actually catch errors which were previously ignored.

This is required for a following commit replacing vfork() with clone3()
and CLONE_VFORK (i.e. not sharing the full memory) .  It should also be
useful to share _metadata to extend expectations to test process's
forks.  For instance, this change identified a wrong expectation in
pidfd_setns_test.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-9-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/kselftest_harness.h | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 8a7d899a75e0..eceedb0a3586 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -430,19 +430,17 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
 			kill(getpid(), WTERMSIG(status)); \
 		__test_check_assert(_metadata); \
 	} \
-	static struct __test_metadata \
-		      _##fixture_name##_##test_name##_object = { \
-		.name = #test_name, \
-		.fn = &wrapper_##fixture_name##_##test_name, \
-		.fixture = &_##fixture_name##_fixture_object, \
-		.termsig = signal, \
-		.timeout = tmout, \
-		.teardown_parent = false, \
-	 }; \
 	static void __attribute__((constructor)) \
 			_register_##fixture_name##_##test_name(void) \
 	{ \
-		__register_test(&_##fixture_name##_##test_name##_object); \
+		struct __test_metadata *object = mmap(NULL, sizeof(*object), \
+			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+		object->name = #test_name; \
+		object->fn = &wrapper_##fixture_name##_##test_name; \
+		object->fixture = &_##fixture_name##_fixture_object; \
+		object->termsig = signal; \
+		object->timeout = tmout; \
+		__register_test(object); \
 	} \
 	static void fixture_name##_##test_name( \
 		struct __test_metadata __attribute__((unused)) *_metadata, \
-- 
2.44.0

Re: [PATCH v2 8/9] selftests/harness: Share _metadata between forked processes

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:30PM +0200, Mickaël Salaün wrote:
> Unconditionally share _metadata between all forked processes, which
> enables to actually catch errors which were previously ignored.
> 
> This is required for a following commit replacing vfork() with clone3()
> and CLONE_VFORK (i.e. not sharing the full memory) .  It should also be
> useful to share _metadata to extend expectations to test process's
> forks.  For instance, this change identified a wrong expectation in
> pidfd_setns_test.
> 
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Cc: Will Drewry <wad@chromium.org>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH v2 9/9] selftests/harness: Fix vfork() side effects

[Mickaël Salaün]

Setting the time namespace with CLONE_NEWTIME returns -EUSERS if the
calling thread shares memory with another thread (because of the shared
vDSO), which is the case when it is created with vfork().

Fix pidfd_setns_test by replacing test harness's vfork() call with a
clone3() call with CLONE_VFORK, and an explicit sharing of the
_metadata and self objects.

Replace _metadata->teardown_parent with a new FIXTURE_TEARDOWN_PARENT()
helper that can replace FIXTURE_TEARDOWN().  This is a cleaner approach
and it enables to selectively share the fixture data between the child
process running tests and the parent process running the fixture
teardown.  This also avoids updating several tests to not rely on the
self object's copy-on-write property (e.g. storing the returned value of
a fork() call).

Cc: Christian Brauner <brauner@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Günther Noack <gnoack@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@intel.com
Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240429130931.2394118-10-mic@digikod.net
---

Changes since v1:
* Split changes (suggested by Kees).
* Improve documentation.
* Remove the static fixture_name##_teardown_parent initialisation to
  false (as suggested by checkpatch.pl).
---
 tools/testing/selftests/kselftest_harness.h | 66 ++++++++++++++++-----
 tools/testing/selftests/landlock/fs_test.c  | 16 ++---
 2 files changed, 57 insertions(+), 25 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index eceedb0a3586..88ae3c2db12f 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -294,6 +294,32 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
  * A bare "return;" statement may be used to return early.
  */
 #define FIXTURE_TEARDOWN(fixture_name) \
+	static const bool fixture_name##_teardown_parent; \
+	__FIXTURE_TEARDOWN(fixture_name)
+
+/**
+ * FIXTURE_TEARDOWN_PARENT()
+ * *_metadata* is included so that EXPECT_*, ASSERT_* etc. work correctly.
+ *
+ * @fixture_name: fixture name
+ *
+ * .. code-block:: c
+ *
+ *     FIXTURE_TEARDOWN_PARENT(fixture_name) { implementation }
+ *
+ * Same as FIXTURE_TEARDOWN() but run this code in a parent process.  This
+ * enables the test process to drop its privileges without impacting the
+ * related FIXTURE_TEARDOWN_PARENT() (e.g. to remove files from a directory
+ * where write access was dropped).
+ *
+ * To make it possible for the parent process to use *self*, share (MAP_SHARED)
+ * the fixture data between all forked processes.
+ */
+#define FIXTURE_TEARDOWN_PARENT(fixture_name) \
+	static const bool fixture_name##_teardown_parent = true; \
+	__FIXTURE_TEARDOWN(fixture_name)
+
+#define __FIXTURE_TEARDOWN(fixture_name) \
 	void fixture_name##_teardown( \
 		struct __test_metadata __attribute__((unused)) *_metadata, \
 		FIXTURE_DATA(fixture_name) __attribute__((unused)) *self, \
@@ -368,10 +394,11 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
  * Very similar to TEST() except that *self* is the setup instance of fixture's
  * datatype exposed for use by the implementation.
  *
- * The @test_name code is run in a separate process sharing the same memory
- * (i.e. vfork), which means that the test process can update its privileges
- * without impacting the related FIXTURE_TEARDOWN() (e.g. to remove files from
- * a directory where write access was dropped).
+ * The _metadata object is shared (MAP_SHARED) with all the potential forked
+ * processes, which enables them to use EXCEPT_*() and ASSERT_*().
+ *
+ * The *self* object is only shared with the potential forked processes if
+ * FIXTURE_TEARDOWN_PARENT() is used instead of FIXTURE_TEARDOWN().
  */
 #define TEST_F(fixture_name, test_name) \
 	__TEST_F_IMPL(fixture_name, test_name, -1, TEST_TIMEOUT_DEFAULT)
@@ -392,39 +419,49 @@ static pid_t __attribute__((__unused__)) clone3_vfork(void)
 		struct __fixture_variant_metadata *variant) \
 	{ \
 		/* fixture data is alloced, setup, and torn down per call. */ \
-		FIXTURE_DATA(fixture_name) self; \
+		FIXTURE_DATA(fixture_name) self_private, *self = NULL; \
 		pid_t child = 1; \
 		int status = 0; \
 		/* Makes sure there is only one teardown, even when child forks again. */ \
 		bool *teardown = mmap(NULL, sizeof(*teardown), \
 			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
 		*teardown = false; \
-		memset(&self, 0, sizeof(FIXTURE_DATA(fixture_name))); \
+		if (sizeof(*self) > 0) { \
+			if (fixture_name##_teardown_parent) { \
+				self = mmap(NULL, sizeof(*self), PROT_READ | PROT_WRITE, \
+					MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+			} else { \
+				memset(&self_private, 0, sizeof(self_private)); \
+				self = &self_private; \
+			} \
+		} \
 		if (setjmp(_metadata->env) == 0) { \
-			/* Use the same _metadata. */ \
-			child = vfork(); \
+			/* _metadata and potentially self are shared with all forks. */ \
+			child = clone3_vfork(); \
 			if (child == 0) { \
-				fixture_name##_setup(_metadata, &self, variant->data); \
+				fixture_name##_setup(_metadata, self, variant->data); \
 				/* Let setup failure terminate early. */ \
 				if (_metadata->exit_code) \
 					_exit(0); \
 				_metadata->setup_completed = true; \
-				fixture_name##_##test_name(_metadata, &self, variant->data); \
+				fixture_name##_##test_name(_metadata, self, variant->data); \
 			} else if (child < 0 || child != waitpid(child, &status, 0)) { \
 				ksft_print_msg("ERROR SPAWNING TEST GRANDCHILD\n"); \
 				_metadata->exit_code = KSFT_FAIL; \
 			} \
 		} \
 		if (child == 0) { \
-			if (_metadata->setup_completed && !_metadata->teardown_parent && \
+			if (_metadata->setup_completed && !fixture_name##_teardown_parent && \
 					__sync_bool_compare_and_swap(teardown, false, true)) \
-				fixture_name##_teardown(_metadata, &self, variant->data); \
+				fixture_name##_teardown(_metadata, self, variant->data); \
 			_exit(0); \
 		} \
-		if (_metadata->setup_completed && _metadata->teardown_parent && \
+		if (_metadata->setup_completed && fixture_name##_teardown_parent && \
 				__sync_bool_compare_and_swap(teardown, false, true)) \
-			fixture_name##_teardown(_metadata, &self, variant->data); \
+			fixture_name##_teardown(_metadata, self, variant->data); \
 		munmap(teardown, sizeof(*teardown)); \
+		if (self && fixture_name##_teardown_parent) \
+			munmap(self, sizeof(*self)); \
 		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
 			/* Forward signal to __wait_for_test(). */ \
 			kill(getpid(), WTERMSIG(status)); \
@@ -895,7 +932,6 @@ struct __test_metadata {
 	bool timed_out;	/* did this test timeout instead of exiting? */
 	bool aborted;	/* stopped test due to failed ASSERT */
 	bool setup_completed; /* did setup finish? */
-	bool teardown_parent; /* run teardown in a parent process */
 	jmp_buf env;	/* for exiting out of test early */
 	struct __test_results *results;
 	struct __test_metadata *prev, *next;
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 1e2cffde02b5..27744524df51 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -286,8 +286,6 @@ static void prepare_layout_opt(struct __test_metadata *const _metadata,
 
 static void prepare_layout(struct __test_metadata *const _metadata)
 {
-	_metadata->teardown_parent = true;
-
 	prepare_layout_opt(_metadata, &mnt_tmp);
 }
 
@@ -316,7 +314,7 @@ FIXTURE_SETUP(layout0)
 	prepare_layout(_metadata);
 }
 
-FIXTURE_TEARDOWN(layout0)
+FIXTURE_TEARDOWN_PARENT(layout0)
 {
 	cleanup_layout(_metadata);
 }
@@ -379,7 +377,7 @@ FIXTURE_SETUP(layout1)
 	create_layout1(_metadata);
 }
 
-FIXTURE_TEARDOWN(layout1)
+FIXTURE_TEARDOWN_PARENT(layout1)
 {
 	remove_layout1(_metadata);
 
@@ -3692,7 +3690,7 @@ FIXTURE_SETUP(ftruncate)
 	create_file(_metadata, file1_s1d1);
 }
 
-FIXTURE_TEARDOWN(ftruncate)
+FIXTURE_TEARDOWN_PARENT(ftruncate)
 {
 	EXPECT_EQ(0, remove_path(file1_s1d1));
 	cleanup_layout(_metadata);
@@ -3870,7 +3868,7 @@ FIXTURE_SETUP(layout1_bind)
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
 
-FIXTURE_TEARDOWN(layout1_bind)
+FIXTURE_TEARDOWN_PARENT(layout1_bind)
 {
 	/* umount(dir_s2d2)) is handled by namespace lifetime. */
 
@@ -4275,7 +4273,7 @@ FIXTURE_SETUP(layout2_overlay)
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
 
-FIXTURE_TEARDOWN(layout2_overlay)
+FIXTURE_TEARDOWN_PARENT(layout2_overlay)
 {
 	if (self->skip_test)
 		SKIP(return, "overlayfs is not supported (teardown)");
@@ -4708,8 +4706,6 @@ FIXTURE_SETUP(layout3_fs)
 		SKIP(return, "this filesystem is not supported (setup)");
 	}
 
-	_metadata->teardown_parent = true;
-
 	prepare_layout_opt(_metadata, &variant->mnt);
 
 	/* Creates directory when required. */
@@ -4743,7 +4739,7 @@ FIXTURE_SETUP(layout3_fs)
 	free(dir_path);
 }
 
-FIXTURE_TEARDOWN(layout3_fs)
+FIXTURE_TEARDOWN_PARENT(layout3_fs)
 {
 	if (self->skip_test)
 		SKIP(return, "this filesystem is not supported (teardown)");
-- 
2.44.0

Re: [PATCH v2 9/9] selftests/harness: Fix vfork() side effects

[Kees Cook]

On Mon, Apr 29, 2024 at 03:09:31PM +0200, Mickaël Salaün wrote:
> Setting the time namespace with CLONE_NEWTIME returns -EUSERS if the
> calling thread shares memory with another thread (because of the shared
> vDSO), which is the case when it is created with vfork().
> 
> Fix pidfd_setns_test by replacing test harness's vfork() call with a
> clone3() call with CLONE_VFORK, and an explicit sharing of the
> _metadata and self objects.
> 
> Replace _metadata->teardown_parent with a new FIXTURE_TEARDOWN_PARENT()
> helper that can replace FIXTURE_TEARDOWN().  This is a cleaner approach
> and it enables to selectively share the fixture data between the child
> process running tests and the parent process running the fixture
> teardown.  This also avoids updating several tests to not rely on the
> self object's copy-on-write property (e.g. storing the returned value of
> a fork() call).
> 
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Günther Noack <gnoack@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Will Drewry <wad@chromium.org>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@intel.com
> Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

Thanks for splitting these up! I found it much more digestible. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook