On Tue, 3 Nov 2020 23:06:14 +0100 Marc Kleine-Budde wrote: > From: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > > 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> Hm... Why do we receive a skb with a socket attached? At a quick glance this is some loopback, so shouldn't we skb_orphan() in the xmit function instead? Otherwise we should probably fix this in enqueue_to_backlog(). > diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c > index b70ded3760f2..73cfcd7e9517 100644 > --- a/drivers/net/can/dev.c > +++ b/drivers/net/can/dev.c > @@ -538,7 +538,11 @@ 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; > }
