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    Subject[PATCH 5.10 052/593] can: isotp: isotp_release(): omit unintended hrtimer restart on socket release
    Date
    From: Oliver Hartkopp <socketcan@hartkopp.net>

    commit 14a4696bc3118ba49da28f79280e1d55603aa737 upstream.

    When closing the isotp socket, the potentially running hrtimers are
    canceled before removing the subscription for CAN identifiers via
    can_rx_unregister().

    This may lead to an unintended (re)start of a hrtimer in
    isotp_rcv_cf() and isotp_rcv_fc() in the case that a CAN frame is
    received by isotp_rcv() while the subscription removal is processed.

    However, isotp_rcv() is called under RCU protection, so after calling
    can_rx_unregister, we may call synchronize_rcu in order to wait for
    any RCU read-side critical sections to finish. This prevents the
    reception of CAN frames after hrtimer_cancel() and therefore the
    unintended (re)start of the hrtimers.

    Link: https://lore.kernel.org/r/20210618173713.2296-1-socketcan@hartkopp.net
    Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
    Cc: linux-stable <stable@vger.kernel.org>
    Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
    Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/can/isotp.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/net/can/isotp.c
    +++ b/net/can/isotp.c
    @@ -1023,9 +1023,6 @@ static int isotp_release(struct socket *

    lock_sock(sk);

    - hrtimer_cancel(&so->txtimer);
    - hrtimer_cancel(&so->rxtimer);
    -
    /* remove current filters & unregister */
    if (so->bound) {
    if (so->ifindex) {
    @@ -1037,10 +1034,14 @@ static int isotp_release(struct socket *
    SINGLE_MASK(so->rxid),
    isotp_rcv, sk);
    dev_put(dev);
    + synchronize_rcu();
    }
    }
    }

    + hrtimer_cancel(&so->txtimer);
    + hrtimer_cancel(&so->rxtimer);
    +
    so->ifindex = 0;
    so->bound = 0;


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