Re: [PATCH] setsourcefilter: Use malloc() rather than alloca().

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

On 11/05/23 12:09, Joe Simmons-Talbott via Libc-alpha wrote:
> To prevent possible stack overflow use malloc() rather than alloca().
> ---
>  sysdeps/unix/sysv/linux/setsourcefilter.c | 22 ++++++----------------
>  1 file changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/setsourcefilter.c b/sysdeps/unix/sysv/linux/setsourcefilter.c
> index 538f4de696..6678572968 100644
> --- a/sysdeps/unix/sysv/linux/setsourcefilter.c
> +++ b/sysdeps/unix/sysv/linux/setsourcefilter.c
> @@ -16,7 +16,6 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <alloca.h>
>  #include <errno.h>
>  #include <stdlib.h>
>  #include <string.h>
> @@ -34,17 +33,11 @@ setsourcefilter (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.  */
>    size_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;
> -    }
> +  gf = (struct group_filter *) malloc (needed);
> +  if (gf == NULL)
> +    return -1;
>  
>    gf->gf_interface = interface;
>    memcpy (&gf->gf_group, group, grouplen);
> @@ -63,12 +56,9 @@ setsourcefilter (int s, uint32_t interface, const struct sockaddr *group,
>    else
>      result = __setsockopt (s, sol, MCAST_MSFILTER, gf, needed);
>  
> -  if (! use_alloca)
> -    {
> -      int save_errno = errno;
> -      free (gf);
> -      __set_errno (save_errno);
> -    }
> +  int save_errno = errno;
> +  free (gf);
> +  __set_errno (save_errno);
>  
>    return result;
>  }

free now must preserve errno (check 69fda43b8dd795c3658869633ca0708ed3134006),
so there is no need to save/restore it.  The rest looks ok for me.