Patch "rxrpc: Restore removed timer deletion" has been added to the 5.17-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rxrpc: Restore removed timer deletion

to the 5.17-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rxrpc-restore-removed-timer-deletion.patch
and it can be found in the queue-5.17 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit bdd5f54b54c8caffed8e811fae98db66ea9820bc
Author: David Howells <dhowells@xxxxxxxxxx>
Date:   Wed Apr 13 11:16:25 2022 +0100

    rxrpc: Restore removed timer deletion
    
    [ 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>

diff --git a/net/rxrpc/net_ns.c b/net/rxrpc/net_ns.c
index f15d6942da45..cc7e30733feb 100644
--- a/net/rxrpc/net_ns.c
+++ b/net/rxrpc/net_ns.c
@@ -113,7 +113,9 @@ 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);