From: David Howells dhowells@redhat.com
[ 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@redhat.com cc: Eric Dumazet edumazet@google.com cc: Marc Dionne marc.dionne@auristor.com cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/20220404183439.3537837-1-eric.dumazet@gmail.com/ [1] Link: https://syzkaller.appspot.com/bug?extid=724378c4bb58f703b09a [2] Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- 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);