This is a note to let you know that I've just added the patch titled can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context to the 5.4-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: can-dev-can_get_echo_skb-prevent-call-to-kfree_skb-i.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 075eb6332098d6a8b0d01af1ae5a99487b8b71ae Author: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> Date: Sat Oct 3 00:41:45 2020 +0900 can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context [ Upstream commit 2283f79b22684d2812e5c76fc2280aae00390365 ] If a driver calls can_get_echo_skb() during a hardware IRQ (which is often, but not always, the case), the 'WARN_ON(in_irq)' in net/core/skbuff.c#skb_release_head_state() might be triggered, under network congestion circumstances, together with the potential risk of a NULL pointer dereference. The root cause of this issue is the call to kfree_skb() instead of dev_kfree_skb_irq() in net/core/dev.c#enqueue_to_backlog(). This patch prevents the skb to be freed within the call to netif_rx() by incrementing its reference count with skb_get(). The skb is finally freed by one of the in-irq-context safe functions: dev_consume_skb_any() or dev_kfree_skb_any(). The "any" version is used because some drivers might call can_get_echo_skb() in a normal context. The reason for this issue to occur is that initially, in the core network stack, loopback skb were not supposed to be received in hardware IRQ context. The CAN stack is an exeption. This bug was previously reported back in 2017 in [1] but the proposed patch never got accepted. While [1] directly modifies net/core/dev.c, we try to propose here a smoother modification local to CAN network stack (the assumption behind is that only CAN devices are affected by this issue). [1] http://lore.kernel.org/r/57a3ffb6-3309-3ad5-5a34-e93c3fe3614d@xxxxxxxxxxx Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> Link: https://lore.kernel.org/r/20201002154219.4887-2-mailhol.vincent@xxxxxxxxxx Fixes: 39549eef3587 ("can: CAN Network device driver and Netlink interface") Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c index 3a33fb5034005..de3c589b1ae0e 100644 --- a/drivers/net/can/dev.c +++ b/drivers/net/can/dev.c @@ -512,7 +512,11 @@ unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx) if (!skb) return 0; - netif_rx(skb); + skb_get(skb); + if (netif_rx(skb) == NET_RX_SUCCESS) + dev_consume_skb_any(skb); + else + dev_kfree_skb_any(skb); return len; }