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From: Brooks Davis <brooks@FreeBSD.org>
Date: Mon, 24 Apr 2017 22:37:54 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r317391 - stable/11/lib/libc/gen
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Author: brooks
Date: Mon Apr 24 22:37:54 2017
New Revision: 317391
URL: https://svnweb.freebsd.org/changeset/base/317391

Log:
  MFC r316768:
  
  Fix an out-of-bounds write when a zero-length buffer is passed.
  
  Found with ttyname_test and CHERI bounds checking.
  
  Reviewed by:	emaste
  Obtained from:	CheriBSD
  Sponsored by:	DARPA, AFRL

Modified:
  stable/11/lib/libc/gen/ttyname.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/lib/libc/gen/ttyname.c
==============================================================================
--- stable/11/lib/libc/gen/ttyname.c	Mon Apr 24 22:35:00 2017	(r317390)
+++ stable/11/lib/libc/gen/ttyname.c	Mon Apr 24 22:37:54 2017	(r317391)
@@ -61,6 +61,10 @@ ttyname_r(int fd, char *buf, size_t len)
 {
 	size_t used;
 
+	/* Don't write off the end of a zero-length buffer. */
+	if (len < 1)
+		return (ERANGE);
+
 	*buf = '\0';
 
 	/* Must be a terminal. */