[PATCH v2] linux: Enforce zero fill of siginfo_t

[mengqinggang]

Can this patch be pushed to master?
tst-pidfd also failed on LoongArch32 without this patch.

Thanks,
Meng


在 2026/1/20 21:13, Adhemerval Zanella 写道:
> The glibc siginfo struct is larger than the kABI one, and the kernel
> enforces that for an unknown si_code, all the extra bytes should be 0
> (post_copy_siginfo_from_user).
>
> For armhf, gcc-15 is fully zero-filling the struct (it seems to be a
> compiler issue, although I haven't found any already registered on
> gcc bugzilla).
>
> In any case, to avoid false positives, force zero-filling on the
> structure.
>
> Checked on arm-linux-gnueabihf.
> --
> Changes from v1:
> * Use memset and add a comment why it is needed.
> ---
>   sysdeps/unix/sysv/linux/tst-pidfd.c | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/tst-pidfd.c b/sysdeps/unix/sysv/linux/tst-pidfd.c
> index d50e36b18a..7dd83e8aa7 100644
> --- a/sysdeps/unix/sysv/linux/tst-pidfd.c
> +++ b/sysdeps/unix/sysv/linux/tst-pidfd.c
> @@ -30,6 +30,7 @@
>   #include <sys/pidfd.h>
>   #include <sys/wait.h>
>   #include <stdlib.h>
> +#include <string.h>
>   #include <unistd.h>
>   
>   #define REMOTE_PATH "/dev/null"
> @@ -210,14 +211,15 @@ do_test (void)
>     /* Wait for second sigtimedwait.  */
>     support_process_state_wait (pid, support_process_state_sleeping);
>     {
> -    siginfo_t info =
> -      {
> -	.si_signo = SIGUSR2,
> -	.si_errno = EAGAIN,
> -	.si_code = -10,
> -	.si_pid = ppid,
> -	.si_uid = puid
> -      };
> +    siginfo_t info;
> +    /* The glibc siginfo struct is larger than the kABI one, and the kernel
> +       enforces that for an unknown si_code, all the extra bytes should be 0.  */
> +    memset (&info, 0, sizeof (info));
> +    info.si_signo = SIGUSR2;
> +    info.si_errno = EAGAIN;
> +    info.si_code = -10;
> +    info.si_pid = ppid;
> +    info.si_uid = puid;
>       TEST_COMPARE (pidfd_send_signal (pidfd, SIGUSR2, &info, 0), 0);
>     }
>