[glibc] getipv4sourcefilter: Get rid of alloca

[glibc] getipv4sourcefilter: Get rid of alloca

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=884012db2046fce17bea0f35210ee424cc60ae06

commit 884012db2046fce17bea0f35210ee424cc60ae06
Author: Joe Simmons-Talbott <josimmon@redhat.com>
Date:   Tue May 30 14:32:55 2023 -0400

    getipv4sourcefilter: Get rid of alloca
    
    Use a scratch_buffer rather than alloca to avoid potential stack
    overflows.
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 sysdeps/unix/sysv/linux/getipv4sourcefilter.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/getipv4sourcefilter.c b/sysdeps/unix/sysv/linux/getipv4sourcefilter.c
index 8a367b1048..ce72becead 100644
--- a/sysdeps/unix/sysv/linux/getipv4sourcefilter.c
+++ b/sysdeps/unix/sysv/linux/getipv4sourcefilter.c
@@ -16,9 +16,9 @@
    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 <scratch_buffer.h>
 #include <string.h>
 #include <stdint.h>
 #include <netinet/in.h>
@@ -33,17 +33,12 @@ getipv4sourcefilter (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.  */
   socklen_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;
@@ -61,12 +56,7 @@ getipv4sourcefilter (int s, struct in_addr interface, struct in_addr group,
       *numsrc = imsf->imsf_numsrc;
     }
 
-  if (! use_alloca)
-    {
-      int save_errno = errno;
-      free (imsf);
-      __set_errno (save_errno);
-    }
+  scratch_buffer_free (&buf);
 
   return result;
 }