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 523e485a11b840b574b3fac3e0e7e6fa23d895e3..0918d3b6df723516080c65b2141ff00f51a77855 100644 (file)
--- 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;
        }