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From: Guy Helmer <ghelmer@FreeBSD.org>
Date: Tue, 6 Nov 2012 21:07:05 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r242673 - head/sys/net
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Author: ghelmer
Date: Tue Nov  6 21:07:04 2012
New Revision: 242673
URL: http://svnweb.freebsd.org/changeset/base/242673

Log:
  Work around a race in bpfread() by validating the hold buffer pointer
  before freeing it. Otherwise, we can lose a buffer and cause a panic
  in catchpacket().

Modified:
  head/sys/net/bpf.c

Modified: head/sys/net/bpf.c
==============================================================================
--- head/sys/net/bpf.c	Tue Nov  6 20:30:23 2012	(r242672)
+++ head/sys/net/bpf.c	Tue Nov  6 21:07:04 2012	(r242673)
@@ -954,10 +954,13 @@ bpfread(struct cdev *dev, struct uio *ui
 	error = bpf_uiomove(d, d->bd_hbuf, d->bd_hlen, uio);
 
 	BPFD_LOCK(d);
-	d->bd_fbuf = d->bd_hbuf;
-	d->bd_hbuf = NULL;
-	d->bd_hlen = 0;
-	bpf_buf_reclaimed(d);
+	if (d->bd_hbuf != NULL) {
+		/* Free the hold buffer only if it is still valid. */
+		d->bd_fbuf = d->bd_hbuf;
+		d->bd_hbuf = NULL;
+		d->bd_hlen = 0;
+		bpf_buf_reclaimed(d);
+	}
 	BPFD_UNLOCK(d);
 
 	return (error);