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From: John Baldwin <jhb@FreeBSD.org>
Date: Wed, 7 Sep 2016 18:08:43 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r305548 - head/sys/dev/cxgbe
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Author: jhb
Date: Wed Sep  7 18:08:43 2016
New Revision: 305548
URL: https://svnweb.freebsd.org/changeset/base/305548

Log:
  Don't break out of the m_advance() loop if len drops to zero.
  
  If a packet contains the Ethernet header (14 bytes) in the first mbuf
  and the payload (IP + UDP + data) in the second mbuf, then the attempt
  to fetch the l3hdr will return a NULL pointer.  The first loop iteration
  will drop len to zero and exit the loop without setting 'p'.  However,
  the desired data is at the start of the second mbuf, so the correct
  behavior is to loop around and let the conditional set 'p' to m_data of
  the next mbuf (and leave offset as 0).
  
  Reviewed by:	np
  Sponsored by:	Chelsio Communications

Modified:
  head/sys/dev/cxgbe/t4_sge.c

Modified: head/sys/dev/cxgbe/t4_sge.c
==============================================================================
--- head/sys/dev/cxgbe/t4_sge.c	Wed Sep  7 18:06:34 2016	(r305547)
+++ head/sys/dev/cxgbe/t4_sge.c	Wed Sep  7 18:08:43 2016	(r305548)
@@ -2082,7 +2082,7 @@ m_advance(struct mbuf **pm, int *poffset
 
 	MPASS(len > 0);
 
-	while (len) {
+	for (;;) {
 		if (offset + len < m->m_len) {
 			offset += len;
 			p = mtod(m, uintptr_t) + offset;