[PATCH 3.16 229/366] libceph: validate con->state at the top of try_write()

Ben Hutchings
2018-10-14T15:25:41Z

From: Ilya Dryomov <idryomov@gmail.com>

commit 9c55ad1c214d9f8c4594ac2c3fa392c1c32431a7 upstream.

ceph_con_workfn() validates con->state before calling try_read() and
then try_write(). However, try_read() temporarily releases con->mutex,
notably in process_message() and ceph_con_in_msg_alloc(), opening the
window for ceph_con_close() to sneak in, close the connection and
release con->sock. When try_write() is called on the assumption that
con->state is still valid (i.e. not STANDBY or CLOSED), a NULL sock
gets passed to the networking stack:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: selinux_socket_sendmsg+0x5/0x20

Make sure con->state is valid at the top of try_write() and add an
explicit BUG_ON for this, similar to try_read().

Link: https://tracker.ceph.com/issues/23706
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ceph/messenger.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -2453,6 +2453,11 @@ static int try_write(struct ceph_connect
int ret = 1;

dout("try_write start %p state %lu\n", con, con->state);
+ if (con->state != CON_STATE_PREOPEN &&
+ con->state != CON_STATE_CONNECTING &&
+ con->state != CON_STATE_NEGOTIATING &&
+ con->state != CON_STATE_OPEN)
+ return 0;

more:
dout("try_write out_kvec_bytes %d\n", con->out_kvec_bytes);
@@ -2478,6 +2483,8 @@ more:
}

more_kvec:
+ BUG_ON(!con->sock);
+
/* kvec data queued? */
if (con->out_skip) {
ret = write_partial_skip(con);