[glibc] setipv4sourcefilter: Avoid using alloca.

[glibc] setipv4sourcefilter: Avoid using alloca.

[Siddhesh Poyarekar]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=02f3d4c53a81f4c9954fbd5502f2e4fe1ab25edd

commit 02f3d4c53a81f4c9954fbd5502f2e4fe1ab25edd
Author: Joe Simmons-Talbott <josimmon@redhat.com>
Date:   Fri May 26 09:58:27 2023 -0400

    setipv4sourcefilter: Avoid using alloca.
    
    Use a scratch_buffer rather than alloca/malloc to avoid potential stack
    overflow.
    
    Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Diff:
---
 sysdeps/unix/sysv/linux/setipv4sourcefilter.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/setipv4sourcefilter.c b/sysdeps/unix/sysv/linux/setipv4sourcefilter.c
index 7f146d789a..8c77ba33bd 100644
--- a/sysdeps/unix/sysv/linux/setipv4sourcefilter.c
+++ b/sysdeps/unix/sysv/linux/setipv4sourcefilter.c
@@ -16,12 +16,12 @@
    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 <scratch_buffer.h>
 #include <sys/socket.h>
 
 
@@ -33,17 +33,12 @@ setipv4sourcefilter (int s, struct in_addr interface, struct in_addr group,
   /* We have to create an struct ip_msfilter object which we can pass
      to the kernel.  */
   size_t needed = IP_MSFILTER_SIZE (numsrc);
-  int use_alloca = __libc_use_alloca (needed);
 
-  struct ip_msfilter *imsf;
-  if (use_alloca)
-    imsf = (struct ip_msfilter *) alloca (needed);
-  else
-    {
-      imsf = (struct ip_msfilter *) malloc (needed);
-      if (imsf == NULL)
-	return -1;
-    }
+  struct scratch_buffer buf;
+  scratch_buffer_init (&buf);
+  if (!scratch_buffer_set_array_size (&buf, 1, needed))
+    return -1;
+  struct ip_msfilter *imsf = buf.data;
 
   imsf->imsf_multiaddr = group;
   imsf->imsf_interface = interface;
@@ -53,12 +48,7 @@ setipv4sourcefilter (int s, struct in_addr interface, struct in_addr group,
 
   int result = __setsockopt (s, SOL_IP, IP_MSFILTER, imsf, needed);
 
-  if (! use_alloca)
-    {
-      int save_errno = errno;
-      free (imsf);
-      __set_errno (save_errno);
-    }
+  scratch_buffer_free (&buf);
 
   return result;
 }