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From: "Bjoern A. Zeeb" <bz@FreeBSD.org>
Date: Tue, 25 Aug 2009 12:32:16 +0000 (UTC)
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Subject: svn commit: r196538 - in stable/7/sys: . contrib/pf kern
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Author: bz
Date: Tue Aug 25 12:32:16 2009
New Revision: 196538
URL: http://svn.freebsd.org/changeset/base/196538

Log:
  MFC r182842:
  
    Catch a possible NULL pointer deref in case the offsets got mangled
    somehow.
    As a consequence we may now get an unexpected result(*).
    Catch that error cases with a well defined panic giving appropriate
    pointers to ease debugging.
  
    (*) While the concensus was that the case should never happen unless
        there was a bug, noone was definitively sure.

Modified:
  stable/7/sys/   (props changed)
  stable/7/sys/contrib/pf/   (props changed)
  stable/7/sys/kern/uipc_sockbuf.c

Modified: stable/7/sys/kern/uipc_sockbuf.c
==============================================================================
--- stable/7/sys/kern/uipc_sockbuf.c	Tue Aug 25 11:44:17 2009	(r196537)
+++ stable/7/sys/kern/uipc_sockbuf.c	Tue Aug 25 12:32:16 2009	(r196538)
@@ -930,11 +930,13 @@ sbsndptr(struct sockbuf *sb, u_int off, 
 
 	/* Advance by len to be as close as possible for the next transmit. */
 	for (off = off - sb->sb_sndptroff + len - 1;
-	     off > 0 && off >= m->m_len;
+	     off > 0 && m != NULL && off >= m->m_len;
 	     m = m->m_next) {
 		sb->sb_sndptroff += m->m_len;
 		off -= m->m_len;
 	}
+	if (off > 0 && m == NULL)
+		panic("%s: sockbuf %p and mbuf %p clashing", __func__, sb, ret);
 	sb->sb_sndptr = m;
 
 	return (ret);