[PATCH] Linux: Use faccessat2 to implement faccessat (bug 18683)

[Adhemerval Zanella]

On 07/08/2020 13:58, Florian Weimer via Libc-alpha wrote:
> This provides correct AT_EACCESS handling and also takes
> Linux security modules into account.
> 
> Tested on i686-linux-gnu, x86_64-linux-gnu.  Built with
> build-many-glibcs.py.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> 
> ---
>  sysdeps/unix/sysv/linux/faccessat.c       | 14 +++++++++++---
>  sysdeps/unix/sysv/linux/kernel-features.h |  8 ++++++++
>  2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/faccessat.c b/sysdeps/unix/sysv/linux/faccessat.c
> index e4f18ab2db..56cb6dcc8b 100644
> --- a/sysdeps/unix/sysv/linux/faccessat.c
> +++ b/sysdeps/unix/sysv/linux/faccessat.c
> @@ -30,6 +30,13 @@
>  int
>  faccessat (int fd, const char *file, int mode, int flag)
>  {
> +  int ret = INLINE_SYSCALL_CALL (faccessat2, fd, file, mode, flag);
> +#if __ASSUME_FACCESSAT2
> +  return ret;
> +#else
> +  if (ret == 0 || errno != ENOSYS)
> +    return ret;
> +
>    if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
>      return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
>  

Ok.

> @@ -41,9 +48,9 @@ faccessat (int fd, const char *file, int mode, int flag)
>      return -1;
>  
>    mode &= (X_OK | W_OK | R_OK);	/* Clear any bogus bits. */
> -#if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
> -# error Oops, portability assumptions incorrect.
> -#endif
> +# if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
> +#  error Oops, portability assumptions incorrect.
> +# endif
>  
>    if (mode == F_OK)
>      return 0;			/* The file exists. */

Ok.

> @@ -68,4 +75,5 @@ faccessat (int fd, const char *file, int mode, int flag)
>      return 0;
>  
>    return INLINE_SYSCALL_ERROR_RETURN_VALUE (EACCES);
> +#endif /* !__ASSUME_FACCESSAT2 */
>  }

Ok.

> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 32533e94cf..a6bbc3c94e 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -214,4 +214,12 @@
>  # define __ASSUME_WAITID_PID0_P_PGID
>  #endif
>  
> +/* The faccessat2 system call was introduced across all architectures
> +   in Linux 5.8.  */
> +#if __LINUX_KERNEL_VERSION >= 0x050800
> +# define __ASSUME_FACCESSAT2 1
> +#else
> +# define __ASSUME_FACCESSAT2 0
> +#endif
> +
>  #endif /* kernel-features.h */
> 

Ok.