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From: Bob Peterson <rpeterso@redhat.com>
To: cluster-devel.redhat.com
Subject: [Cluster-devel] [GFS2 PATCH] GFS2: Fix use-after-free race when calling gfs2_remove_from_ail
Date: Tue, 10 Dec 2013 12:06:35 -0500 (EST)	[thread overview]
Message-ID: <2108655672.39417861.1386695195458.JavaMail.root@redhat.com> (raw)
In-Reply-To: <1170291767.39415863.1386695088991.JavaMail.root@redhat.com>

Hi,

Function gfs2_remove_from_ail drops the reference on the bh via
brelse. This patch fixes a race condition whereby bh is deferenced
after the brelse when setting bd->bd_blkno = bh->b_blocknr;
Under certain rare circumstances, bh might be gone or reused,
and bd->bd_blkno is set to whatever that memory happens to be,
which is often 0. Later, in gfs2_trans_add_unrevoke, that bd fails
the test "bd->bd_blkno >= blkno" which causes it to never be freed.
The end result is that the bd is never freed from the bufdata cache,
which results in this error:
slab error in kmem_cache_destroy(): cache `gfs2_bufdata': Can't free all objects

Regards,

Bob Peterson
Red Hat File Systems

Signed-off-by: Bob Peterson <rpeterso@redhat.com> 
---
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 610613f..9dcb977 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -551,10 +551,10 @@ void gfs2_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	struct buffer_head *bh = bd->bd_bh;
 	struct gfs2_glock *gl = bd->bd_gl;
 
-	gfs2_remove_from_ail(bd);
-	bd->bd_bh = NULL;
 	bh->b_private = NULL;
 	bd->bd_blkno = bh->b_blocknr;
+	gfs2_remove_from_ail(bd); /* drops ref on bh */
+	bd->bd_bh = NULL;
 	bd->bd_ops = &gfs2_revoke_lops;
 	sdp->sd_log_num_revoke++;
 	atomic_inc(&gl->gl_revokes);



       reply	other threads:[~2013-12-10 17:06 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1170291767.39415863.1386695088991.JavaMail.root@redhat.com>
2013-12-10 17:06 ` Bob Peterson [this message]
2013-12-10 17:09   ` [Cluster-devel] [GFS2 PATCH] GFS2: Fix use-after-free race when calling gfs2_remove_from_ail Steven Whitehouse

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