[CC += libc-alpha] Hi Alexander,
On Tue, Jan 20, 2026 at 11:10:07AM +0000, Alexander Atanasov wrote:
> While compiling filesystem selftests there is a warning:
> anon_inode_test.c:45:37: warning: null passed to a callee that
> requires a non-null argument [-Wnonnull]
> 45 | ASSERT_LT(execveat(fd_context, "", NULL, NULL, AT_EMPTY_PATH), 0);
>
> Kernel code is okay to be passed NULL for argv, in which
> case it generates argv by itself inside do_execveat_common.
> Man page of execvat lists both argv and envp as _Nullable.
Yup; the manual page uses that to document that Linux accepts NULL.
> But system's unistd.h says different:
> extern int execveat (int __fd, const char *__path, char *const __argv[],
> char *const __envp[], int __flags)
> __THROW __nonnull ((2, 3));
Hmmmm, this would trigger UB for user-space users relying on the fact
that Linux accepts NULL. Maybe when compiled for Linux, the glibc
headers should remove the [[gnu::nonnull()]] attribute here.
Have a lovely day!
Alex
> (checked ubuntu 24.04 and fedora 43)
>
> Which is the reason for the compiler warning.
>
> Fix the warning by passing a proper argv array.
>
> Fixes: f8ca403ae77cb ("selftests/filesystems: add exec() test for anonymous
> inodes")
> Cc: Christian Brauner <[email protected]>
> Cc: Guenter Roeck <[email protected]>
> Cc: Michael Kerrisk <[email protected]>
> Cc: Alejandro Colomar <[email protected]>
> Cc: Clint George <[email protected]>
> Cc: Ranganath V N <[email protected]>
> Signed-off-by: Alexander Atanasov <[email protected]>
> ---
> tools/testing/selftests/filesystems/anon_inode_test.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> Quote from execv's man referenced from execveat's:
> On Linux, argv and envp can be specified as NULL.
> In both cases, this has the same effect as specifying the argument as a
> pointer
> to a list containing a single null pointer.
> ***Do not take advantage of this nonstandard and nonportable misfeature!***
>
> Listed as possible to pass NULL, then a big fat warning in the man page
> and a header that acctually marks this as invalid usage.
> I failed to find the origin of the above contradiction.
> It looks like POSIX/GNU/Linux missalignment.
> I am putting this here for the record. So may be someone could step in
> and make it right.
>
> I've Cc-ed people who made fixes but they are just compile fixes, no
> explanation of why the warning exists and in most of them the array is not a
> proper
> argv.
>
> diff --git a/tools/testing/selftests/filesystems/anon_inode_test.c
> b/tools/testing/selftests/filesystems/anon_inode_test.c
> index 94c6c81c2301..191549a4304d 100644
> --- a/tools/testing/selftests/filesystems/anon_inode_test.c
> +++ b/tools/testing/selftests/filesystems/anon_inode_test.c
> @@ -4,6 +4,7 @@
>
> #include <fcntl.h>
> #include <stdio.h>
> +#include <unistd.h>
> #include <sys/stat.h>
>
> #include "kselftest_harness.h"
> @@ -37,12 +38,13 @@ TEST(anon_inode_no_chmod)
>
> TEST(anon_inode_no_exec)
> {
> + char *const argv[] = { "", NULL };
> int fd_context;
>
> fd_context = sys_fsopen("tmpfs", 0);
> ASSERT_GE(fd_context, 0);
>
> - ASSERT_LT(execveat(fd_context, "", NULL, NULL, AT_EMPTY_PATH), 0);
> + ASSERT_LT(execveat(fd_context, "", argv, NULL, AT_EMPTY_PATH), 0);
> ASSERT_EQ(errno, EACCES);
>
> EXPECT_EQ(close(fd_context), 0);
> --
> 2.43.0
>
--
<https://www.alejandro-colomar.es>
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