[v2] ceph: fix potential race in ceph_check_caps
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Message ID 20200326132526.15639-1-jlayton@kernel.org
State New
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Series
  • [v2] ceph: fix potential race in ceph_check_caps
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Commit Message

Jeff Layton March 26, 2020, 1:25 p.m. UTC
Nothing ensures that session will still be valid by the time we
dereference the pointer. Take and put a reference.

In principle, we should always be able to get a reference here, but
throw a warning if that's ever not the case.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/ceph/caps.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

Patch
diff mbox series

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 80bde0024615..f8b51d0c8184 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2045,12 +2045,24 @@  void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 			if (mutex_trylock(&session->s_mutex) == 0) {
 				dout("inverting session/ino locks on %p\n",
 				     session);
+				session = ceph_get_mds_session(session);
 				spin_unlock(&ci->i_ceph_lock);
 				if (took_snap_rwsem) {
 					up_read(&mdsc->snap_rwsem);
 					took_snap_rwsem = 0;
 				}
-				mutex_lock(&session->s_mutex);
+				if (session) {
+					mutex_lock(&session->s_mutex);
+					ceph_put_mds_session(session);
+				} else {
+					/*
+					 * Because we take the reference while
+					 * holding the i_ceph_lock, it should
+					 * never be NULL. Throw a warning if it
+					 * ever is.
+					 */
+					WARN_ON_ONCE(true);
+				}
 				goto retry;
 			}
 		}