From: Yiwen Jiang <jiangyiwen@huawei.com>
Date: Fri, 4 Sep 2015 22:44:37 +0000 (-0700)
Subject: ocfs2: avoid access invalid address when read o2dlm debug messages
X-Git-Tag: v4.1.12-92~39^2~16
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=7365cd6504067b01485945506dec93fa9863c59c;p=users%2Fjedix%2Flinux-maple.git

ocfs2: avoid access invalid address when read o2dlm debug messages

The following case will lead to a lockres is freed but is still in use.

cat /sys/kernel/debug/o2dlm/locking_state	dlm_thread
lockres_seq_start
    -> lock dlm->track_lock
    -> get resA
                                                resA->refs decrease to 0,
                                                call dlm_lockres_release,
                                                and wait for "cat" unlock.
Although resA->refs is already set to 0,
increase resA->refs, and then unlock
                                                lock dlm->track_lock
                                                    -> list_del_init()
                                                    -> unlock
                                                    -> free resA

In such a race case, invalid address access may occurs.  So we should
delete list res->tracking before resA->refs decrease to 0.

Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
Reviewed-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit f57a22ddecd6f26040a67e2c12880f98f88b6e00)

Orabug: 24939243

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
---

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 523e485a11b8..0918d3b6df72 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -795,8 +795,18 @@ lookup:
 		dlm_lockres_grab_inflight_ref(dlm, tmpres);
 
 		spin_unlock(&tmpres->spinlock);
-		if (res)
+		if (res) {
+			spin_lock(&dlm->track_lock);
+			if (!list_empty(&res->tracking))
+				list_del_init(&res->tracking);
+			else
+				mlog(ML_ERROR, "Resource %.*s not "
+						"on the Tracking list\n",
+						res->lockname.len,
+						res->lockname.name);
+			spin_unlock(&dlm->track_lock);
 			dlm_lockres_put(res);
+		}
 		res = tmpres;
 		goto leave;
 	}