[Devel] [PATCH VZ10] fs/fuse kio: don't touch sio in pcs_sockio_xmit() after connection abort

[Liu Kui <kui.liu@virtuozzo.com>]

pcs_sockio_xmit() calls pcs_sockio_recv() and then unconditionally
pcs_sockio_send() on the same sio. If recv hits a socket error, it
calls sio_abort(), which leads to call_rcu(sio_destroy_rcu). Since
pcs_sockio_xmit() is not inside an RCU read-side critical section,
so the grace period may elapse and sio may be freed before (or while)
pcs_sockio_send() dereferences it, a narrow use-after-free window.

rpc_abort() clears ep->conn under ep->mutex before destructing the
ioconn, and pcs_sockio_xmit() runs under the same mutex, so recheck
ep->conn after recv and skip the send if the connection is gone.

https://virtuozzo.atlassian.net/browse/VSTOR-141422

Signed-off-by: Liu Kui <kui.liu@virtuozzo.com>
---
 fs/fuse/kio/pcs/pcs_sock_io.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/kio/pcs/pcs_sock_io.c b/fs/fuse/kio/pcs/pcs_sock_io.c
index 47ddc8a7072d..d1f1560db6d2 100644
--- a/fs/fuse/kio/pcs/pcs_sock_io.c
+++ b/fs/fuse/kio/pcs/pcs_sock_io.c
@@ -458,7 +458,14 @@ static void pcs_sockio_xmit(struct pcs_netio *netio)
 
 	sio->flags &= ~(PCS_SOCK_F_POOLOUT|PCS_SOCK_F_POOLIN);
 	pcs_sockio_recv(sio);
-	pcs_sockio_send(sio);
+
+	/* pcs_sockio_recv() may abort the connection: sio_abort() -> eof -> rpc_abort(),
+	 * which resets ep->conn and then destructs sio (freed after an RCU grace period
+	 * we are not part of). ep->conn is reset under ep->mutex, which we hold, so
+	 * recheck it before touching sio again.
+	 */
+	if (likely(ep->conn))
+		pcs_sockio_send(sio);
 }
 
 static int pcs_sockio_flush(struct pcs_netio *netio)
-- 
2.50.1 (Apple Git-155)