[PATCH AUTOSEL 4.14 116/127] ceph: fix potential race in ceph_check_caps

Sasha Levin
2020-09-18T02:30:34Z

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit dc3da0461cc4b76f2d0c5b12247fcb3b520edbbf ]

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>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ceph/caps.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 589cfe3ed873b..ce94d09f6abf9 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1906,12 +1906,24 @@ ack:
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;
}
}
--
2.25.1