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From: Michael Tuexen <tuexen@FreeBSD.org>
Date: Wed, 25 Oct 2017 09:12:22 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r324971 - head/sys/netinet
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Author: tuexen
Date: Wed Oct 25 09:12:22 2017
New Revision: 324971
URL: https://svnweb.freebsd.org/changeset/base/324971

Log:
  Fix a bug reported by Felix Weinrank using the libfuzzer on the
  userland stack.
  
  MFC after:	3 days

Modified:
  head/sys/netinet/sctp_auth.c

Modified: head/sys/netinet/sctp_auth.c
==============================================================================
--- head/sys/netinet/sctp_auth.c	Wed Oct 25 05:55:13 2017	(r324970)
+++ head/sys/netinet/sctp_auth.c	Wed Oct 25 09:12:22 2017	(r324971)
@@ -1606,9 +1606,9 @@ sctp_zero_m(struct mbuf *m, uint32_t m_offset, uint32_
 	/* now use the rest of the mbuf chain */
 	while ((m_tmp != NULL) && (size > 0)) {
 		data = mtod(m_tmp, uint8_t *)+m_offset;
-		if (size > (uint32_t)SCTP_BUF_LEN(m_tmp)) {
-			memset(data, 0, SCTP_BUF_LEN(m_tmp));
-			size -= SCTP_BUF_LEN(m_tmp);
+		if (size > (uint32_t)(SCTP_BUF_LEN(m_tmp) - m_offset)) {
+			memset(data, 0, SCTP_BUF_LEN(m_tmp) - m_offset);
+			size -= SCTP_BUF_LEN(m_tmp) - m_offset;
 		} else {
 			memset(data, 0, size);
 			size = 0;