Re: [PATCH] setsourcefilter: Replace alloca with a scratch_buffer.

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

On 16/05/23 10:45, Joe Simmons-Talbott wrote:
> Use a scratch_buffer rather than either alloca or malloc to reduce the
> possibility of a stack overflow.
> 
> Suggested-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>

LGTM, thanks.

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

> ---
>  sysdeps/unix/sysv/linux/setsourcefilter.c | 27 ++++++-----------------
>  1 file changed, 7 insertions(+), 20 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/setsourcefilter.c b/sysdeps/unix/sysv/linux/setsourcefilter.c
> index 538f4de696..479744f169 100644
> --- a/sysdeps/unix/sysv/linux/setsourcefilter.c
> +++ b/sysdeps/unix/sysv/linux/setsourcefilter.c
> @@ -16,13 +16,10 @@
>     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>
> -#include <stdint.h>
>  #include <netinet/in.h>
> -#include <sys/socket.h>
> +#include <scratch_buffer.h>
>  #include "getsourcefilter.h"
>  
>  
> @@ -34,17 +31,12 @@ 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;
> -    }
> +  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);
> @@ -63,12 +55,7 @@ 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);
> -    }
> +  scratch_buffer_free (&buf);
>  
>    return result;
>  }