[PATCH] syslog() segv fix under memory shortage

[Jakub Jelinek]

On Thu, Apr 15, 2004 at 08:14:03PM +0900, GOTO Masanori wrote:
> This patch fixes misc/syslog.c:vsyslog() segv.  When memory is
> shortage, open_memstream() in vsyslog() can't allocate buffer, and
> then uses local buffer "failbuf".  At last in vsyslog(), free() is
> called everytime even for local buffer, then it goes segv.  This patch
> adds a flag that indicates the buffer is local or not.

__libc_cleanup_push/pop cannot be used that way.
It would expand to:
if (__builtin_expect(need_free, 1))
  do {
    magic;
(void)__writev (...);
if (__builtin_expect(need_free, 1))
  some_more_magic;
} while (0)

How about this instead:

2004-04-16  Jakub Jelinek  <jakub@redhat.com>

	* misc/syslog.c (vsyslog): Avoid freeing failbuf.

--- libc/misc/syslog.c.jj	2003-09-25 17:44:37.000000000 +0200
+++ libc/misc/syslog.c	2004-04-15 19:17:21.069878549 +0200
@@ -237,7 +237,7 @@ vsyslog(pri, fmt, ap)
 		    v->iov_len = 1;
 		  }
 
-		__libc_cleanup_push (free, buf);
+		__libc_cleanup_push (free, buf == failbuf ? NULL : buf);
 
 		/* writev is a cancellation point.  */
 		(void)__writev(STDERR_FILENO, iov, v - iov + 1);
@@ -305,7 +305,8 @@ vsyslog(pri, fmt, ap)
 	__libc_cleanup_pop (0);
 	__libc_lock_unlock (syslog_lock);
 
-	free (buf);
+	if (buf != failbuf)
+		free (buf);
 }
 libc_hidden_def (vsyslog)
 

	Jakub