Re: [PATCH] getsourcefilter: Get rid of alloca.

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 30/05/23 15:13, Joe Simmons-Talbott via Libc-alpha wrote:
> Use a scratch_buffer rather than alloca to avoid potential stack
> overflows.

LGTM, thanks.

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

> ---
>  sysdeps/unix/sysv/linux/getsourcefilter.c | 24 +++++++----------------
>  1 file changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/getsourcefilter.c b/sysdeps/unix/sysv/linux/getsourcefilter.c
> index b9ba58c23a..461ad889a9 100644
> --- a/sysdeps/unix/sysv/linux/getsourcefilter.c
> +++ b/sysdeps/unix/sysv/linux/getsourcefilter.c
> @@ -16,10 +16,10 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <alloca.h>
>  #include <assert.h>
>  #include <errno.h>
>  #include <stdlib.h>
> +#include <scratch_buffer.h>
>  #include <string.h>
>  #include <stdint.h>
>  #include <netatalk/at.h>
> @@ -95,17 +95,12 @@ getsourcefilter (int s, uint32_t interface, const struct sockaddr *group,
>    /* We have to create an struct ip_msfilter object which we can pass
>       to the kernel.  */
>    socklen_t needed = GROUP_FILTER_SIZE (*numsrc);
> -  int use_alloca = __libc_use_alloca (needed);
>  
> -  struct group_filter *gf;
> -  if (use_alloca)
> -    gf = (struct group_filter *) alloca (needed);
> -  else
> -    {
> -      gf = (struct group_filter *) malloc (needed);
> -      if (gf == NULL)
> -	return -1;
> -    }
> +  struct scratch_buffer buf;
> +  scratch_buffer_init (&buf);
> +  if (!scratch_buffer_set_array_size (&buf, 1, needed))
> +    return -1;
> +  struct group_filter *gf = buf.data;
>  
>    gf->gf_interface = interface;
>    memcpy (&gf->gf_group, group, grouplen);
> @@ -135,12 +130,7 @@ getsourcefilter (int s, uint32_t interface, const struct sockaddr *group,
>  	}
>      }
>  
> -  if (! use_alloca)
> -    {
> -      int save_errno = errno;
> -      free (gf);
> -      __set_errno (save_errno);
> -    }
> +  scratch_buffer_free (&buf);
>  
>    return result;
>  }