1 files changed, 18 insertions, 2 deletions
diff --git a/lib/libc/stdio/fwrite.c b/lib/libc/stdio/fwrite.c
index cf52e42..acac943 100644
--- a/lib/libc/stdio/fwrite.c
+++ b/lib/libc/stdio/fwrite.c
@@ -37,6 +37,8 @@ static char sccsid[] = "@(#)fwrite.c	8.1 (Berkeley) 6/4/93";
 __FBSDID("$FreeBSD$");
 
 #include "namespace.h"
+#include <errno.h>
+#include <stdint.h>
 #include <stdio.h>
 #include "un-namespace.h"
 #include "local.h"
@@ -60,10 +62,24 @@ fwrite(buf, size, count, fp)
 	/*
 	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
 	 */
-	n = count * size;
-	if (n == 0)
+	if ((count == 0) || (size == 0))
 		return (0);
 
+	/*
+	 * Check for integer overflow.  As an optimization, first check that
+	 * at least one of {count, size} is at least 2^16, since if both
+	 * values are less than that, their product can't possible overflow
+	 * (size_t is always at least 32 bits on FreeBSD).
+	 */
+	if (((count | size) > 0xFFFF) &&
+	    (count > SIZE_MAX / size)) {
+		errno = EINVAL;
+		fp->_flags |= __SERR;
+		return (0);
+	}
+
+	n = count * size;
+
 	iov.iov_base = (void *)buf;
 	uio.uio_resid = iov.iov_len = n;
 	uio.uio_iov = &iov;