From: David Howells <dhowells@xxxxxxxxxx>
[ Upstream commit ee3b0826b4764f6c13ad6db67495c5a1c38e9025 ]
A recent patch[1] from Eric Dumazet flipped the order in which the
keepalive timer and the keepalive worker were cancelled in order to fix a
syzbot reported issue[2]. Unfortunately, this enables the mirror image bug
whereby the timer races with rxrpc_exit_net(), restarting the worker after
it has been cancelled:
CPU 1 CPU 2
=============== =====================
if (rxnet->live)
<INTERRUPT>
rxnet->live = false;
cancel_work_sync(&rxnet->peer_keepalive_work);
rxrpc_queue_work(&rxnet->peer_keepalive_work);
del_timer_sync(&rxnet->peer_keepalive_timer);
Fix this by restoring the removed del_timer_sync() so that we try to remove
the timer twice. If the timer runs again, it should see ->live == false
and not restart the worker.
Fixes: 1946014ca3b1 ("rxrpc: fix a race in rxrpc_exit_net()")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20220404183439.3537837-1-eric.dumazet@xxxxxxxxx/ [1]
Link: https://syzkaller.appspot.com/bug?extid=724378c4bb58f703b09a [2]
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/rxrpc/net_ns.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/rxrpc/net_ns.c b/net/rxrpc/net_ns.c
index 1b403c2573da..39579cfcf9b8 100644
--- a/net/rxrpc/net_ns.c
+++ b/net/rxrpc/net_ns.c
@@ -117,7 +117,9 @@ static __net_exit void rxrpc_exit_net(struct net *net)
struct rxrpc_net *rxnet = rxrpc_net(net);
rxnet->live = false;
+ del_timer_sync(&rxnet->peer_keepalive_timer);
cancel_work_sync(&rxnet->peer_keepalive_work);
+ /* Remove the timer again as the worker may have restarted it. */
del_timer_sync(&rxnet->peer_keepalive_timer);
rxrpc_destroy_all_calls(rxnet);
rxrpc_destroy_all_connections(rxnet);
--
2.35.1
