1 files changed, 9 insertions, 3 deletions

diff --git a/src/lib/libc/string/strlcat.c b/src/lib/libc/string/strlcat.c
index 073b0d4259..410f448b56 100644
--- a/src/lib/libc/string/strlcat.c
+++ b/src/lib/libc/string/strlcat.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: strlcat.c,v 1.16 2015/08/31 02:53:57 guenther Exp $   */
+/*      $OpenBSD: strlcat.c,v 1.17 2016/10/14 18:19:04 dtucker Exp $    */
 
 /*
  * Copyright (c) 1998, 2015 Todd C. Miller <Todd.Miller@courtesan.com>
@@ -18,6 +18,7 @@
 
 #include <sys/types.h>
 #include <string.h>
+#include <stdint.h>
 
 /*
  * Appends src to string dst of size dsize (unlike strncat, dsize is the
@@ -37,7 +38,7 @@ strlcat(char *dst, const char *src, size_t dsize)
         /* Find the end of dst and adjust bytes left but don't go past end. */
         while (n-- != 0 && *dst != '\0')
                 dst++;
-        dlen = dst - odst;
+        dlen = (uintptr_t)dst - (uintptr_t)odst;
         n = dsize - dlen;
 
         if (n-- == 0)
@@ -51,6 +52,11 @@ strlcat(char *dst, const char *src, size_t dsize)
         }
         *dst = '\0';
 
-        return(dlen + (src - osrc));    /* count does not include NUL */
+        /*
+         * Cast pointers to unsigned type before calculation, to avoid signed
+         * overflow when the string ends where the MSB has changed.
+         * Return value does not include NUL.
+         */
+        return (dlen + ((uintptr_t)src - (uintptr_t)osrc));
 }
 DEF_WEAK(strlcat);