CVE-2020-36789

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context

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 s

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References