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For an rx op subscribed on all interfaces (ifindex == 0), the same op is registered once in the shared per-netns wildcard filter list, so bcm_rx_handler() can run concurrently on different CPUs for frames arriving on different net devices. op->rx_stamp and op->rx_ifindex were written before bcm_rx_update_lock was taken, allowing concurrent writers to race each other - including a torn store of the 64-bit rx_stamp on 32-bit platforms. Beyond a torn store bcm_send_to_user() must report the timestamp/ifindex of the very same frame whose content it is delivering. So the assignment is placed in the same unbroken bcm_rx_update_lock section as the content comparison. As a side effect, the RTR-request frame feature (which never reach bcm_send_to_user()) no longer updates rx_stamp/rx_ifindex, since only the notification path needs them. Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol") Reported-by: sashiko-bot@kernel.org Closes: https://lore.kernel.org/linux-can/20260707145135.5BC831F00A3A@smtp.kernel.org/ Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260714-bcm_fixes-v15-10-562f7e3e42da@hartkopp.net Cc: stable@kernel.org Signed-off-by: Marc Kleine-Budde Signed-off-by: Oliver Hartkopp --- net/can/bcm.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/net/can/bcm.c b/net/can/bcm.c index 4afc2ed..0db9c48 100644 --- a/net/can/bcm.c +++ b/net/can/bcm.c @@ -756,11 +756,6 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data) /* disable timeout */ hrtimer_cancel(&op->timer); - /* save rx timestamp */ - op->rx_stamp = skb->tstamp; - /* save originator for recvfrom() */ - op->rx_ifindex = skb->dev->ifindex; - /* op->flags/op->frames may be updated concurrently by bcm_rx_setup() */ spin_lock_bh(&op->bcm_rx_update_lock); @@ -784,6 +779,14 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data) */ bcm_update_rx_stats(op); + /* save rx timestamp and originator for recvfrom() under lock. + * For an op subscribed on all interfaces (ifindex == 0) + * bcm_rx_handler() can run concurrently on different CPUs so + * the CAN content and the meta data must be bundled correctly. + */ + op->rx_stamp = skb->tstamp; + op->rx_ifindex = skb->dev->ifindex; + if (op->flags & RX_FILTER_ID) { /* the easiest case */ bcm_rx_update_and_send(op, op->last_frames, rxframe); -- 2.43.0