svn commit: r275665 - head/lib/libc/stdio

[Xin LI]

Author: delphij
Date: Wed Dec 10 08:18:22 2014
New Revision: 275665
URL: https://svnweb.freebsd.org/changeset/base/275665

Log:
  In r268924 __fflush was modified so that when write(2) was not successful,
  _p and _w are adjusted to account for the partial write (if any).
  
  However, _p and _w should not be unconditionally adjusted and should only
  be changed when we actually wrote some bytes, or the accumulated accounting
  error will eventually result in a heap buffer overflow.
  
  Reported by:	adrian and alfred (Norse Corporation)
  Security:	FreeBSD-SA-14:27.stdio
  Security:	CVE-2014-8611

Modified:
  head/lib/libc/stdio/fflush.c

Modified: head/lib/libc/stdio/fflush.c
==============================================================================
--- head/lib/libc/stdio/fflush.c	Wed Dec 10 06:43:16 2014	(r275664)
+++ head/lib/libc/stdio/fflush.c	Wed Dec 10 08:18:22 2014	(r275665)
@@ -124,11 +124,13 @@ __sflush(FILE *fp)
 		t = _swrite(fp, (char *)p, n);
 		if (t <= 0) {
 			/* Reset _p and _w. */
-			if (p > fp->_p)	/* Some was written. */
+			if (p > fp->_p) {
+				/* Some was written. */
 				memmove(fp->_p, p, n);
-			fp->_p += n;
-			if ((fp->_flags & (__SLBF | __SNBF)) == 0)
-				fp->_w -= n;
+				fp->_p += n;
+				if ((fp->_flags & (__SLBF | __SNBF)) == 0)
+					fp->_w -= n;
+			}
 			fp->_flags |= __SERR;
 			return (EOF);
 		}