From 2283f79b22684d2812e5c76fc2280aae00390365 Mon Sep 17 00:00:00 2001

From: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

Date: Sat, 3 Oct 2020 00:41:45 +0900

Subject: [PATCH] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context

Git-commit: 2283f79b22684d2812e5c76fc2280aae00390365

Patch-mainline: v5.10-rc3

References: git-fixes

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@cetitec.com

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

Link: https://lore.kernel.org/r/20201002154219.4887-2-mailhol.vincent@wanadoo.fr

Fixes: 39549eef3587 ("can: CAN Network device driver and Netlink interface")

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 drivers/net/can/dev.c | 6 +++++-

 1 file changed, 5 insertions(+), 1 deletion(-)

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;

 }

-- 

2.16.4