[glibc] check_native: Get rid of alloca

[glibc] check_native: Get rid of alloca

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9a17a193b4ea5730aed0b9e532ae741418dd10d3

commit 9a17a193b4ea5730aed0b9e532ae741418dd10d3
Author: Joe Simmons-Talbott <josimmon@redhat.com>
Date:   Tue Jun 13 10:05:03 2023 -0400

    check_native: Get rid of alloca
    
    Use malloc rather than alloca to avoid potential stack overflow.
    
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 sysdeps/unix/sysv/linux/check_native.c | 35 +++++++++++-----------------------
 1 file changed, 11 insertions(+), 24 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/check_native.c b/sysdeps/unix/sysv/linux/check_native.c
index 34876ca624..c4aaf4af19 100644
--- a/sysdeps/unix/sysv/linux/check_native.c
+++ b/sysdeps/unix/sysv/linux/check_native.c
@@ -48,11 +48,20 @@ __check_native (uint32_t a1_index, int *a1_native,
   nladdr.nl_family = AF_NETLINK;
 
   socklen_t addr_len = sizeof (nladdr);
-  bool use_malloc = false;
 
   if (fd < 0)
     return;
 
+  /* Netlink requires that user buffer needs to be either 8kb or page size
+     (whichever is bigger), however this has been changed over time and now
+     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
+     linux/include/linux/netlink.h).  */
+  const size_t buf_size = 8192;
+  char *buf = malloc (buf_size);
+
+  if (buf == NULL)
+    goto out;
+
   if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) != 0
       || __getsockname (fd, (struct sockaddr *) &nladdr, &addr_len) != 0)
     goto out;
@@ -81,26 +90,6 @@ __check_native (uint32_t a1_index, int *a1_native,
   memset (&nladdr, '\0', sizeof (nladdr));
   nladdr.nl_family = AF_NETLINK;
 
-#ifdef PAGE_SIZE
-  /* Help the compiler optimize out the malloc call if PAGE_SIZE
-     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
-  const size_t buf_size = PAGE_SIZE;
-#else
-  const size_t buf_size = __getpagesize ();
-#endif
-  char *buf;
-
-  if (__libc_use_alloca (buf_size))
-    buf = alloca (buf_size);
-  else
-    {
-      buf = malloc (buf_size);
-      if (buf != NULL)
-	use_malloc = true;
-      else
-	goto out;
-    }
-
   struct iovec iov = { buf, buf_size };
 
   if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
@@ -170,7 +159,5 @@ __check_native (uint32_t a1_index, int *a1_native,
 
 out:
   __close_nocancel_nostatus (fd);
-
-  if (use_malloc)
-    free (buf);
+  free (buf);
 }