CVE-2020-36789 Affecting kernel-rt-debug-modules package, versions *


Severity

Recommended
0.0
medium
0
10

Based on Red Hat Enterprise Linux security rating.

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  • Snyk IDSNYK-RHEL8-KERNELRTDEBUGMODULES-9784197
  • published19 Apr 2025
  • disclosed17 Apr 2025

Introduced: 17 Apr 2025

NewCVE-2020-36789  (opens in a new tab)

How to fix?

There is no fixed version for RHEL:8 kernel-rt-debug-modules.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-rt-debug-modules package and not the kernel-rt-debug-modules package as distributed by RHEL. See How to fix? for RHEL:8 relevant fixed versions and status.

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 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

CVSS Base Scores

version 3.1