diff mbox series

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

Message ID 20240429130931.2394118-5-mic@digikod.net (mailing list archive)
State New
Headers show
Series Fix Kselftest's vfork() side effects | expand

Commit Message

Mickaël Salaün April 29, 2024, 1:09 p.m. UTC
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(-)

Comments

Kees Cook April 29, 2024, 3:52 p.m. UTC | #1
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>
Jakub Kicinski April 29, 2024, 5:16 p.m. UTC | #2
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
Mickaël Salaün April 29, 2024, 7:18 p.m. UTC | #3
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.
diff mbox series

Patch

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;