[PATCH] setsourcefilter: Replace alloca with a scratch_buffer.

[Joe Simmons-Talbott <josimmon@redhat.com>]

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>
---
 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;
 }
-- 
2.39.2