Linux Kernel up to 5.9.8 net/core/skbuff.c can_get_echo_skb reference count

Summaryinfo

A vulnerability was found in Linux Kernel up to 5.9.8 and classified as critical. Affected is the function can_get_echo_skb of the file net/core/skbuff.c. The manipulation results in reference count. This vulnerability was named CVE-2020-36789. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 5.9.8. Affected is the function can_get_echo_skb of the file net/core/skbuff.c. The manipulation with an unknown input leads to a reference count vulnerability. CWE is classifying the issue as CWE-911. The product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. This is going to have an impact on availability. CVE summarizes:

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/[email protected]

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2020-36789 since 02/26/2024. The exploitability is told to be difficult. There are known technical details, but no exploit is available.

Upgrading to version 4.4.244, 4.9.244, 4.14.207, 4.19.158, 5.4.78 or 5.9.9 eliminates this vulnerability. Applying the patch 248b71ce92d4f3a574b2537f9838f48e892618f4/451187b20431924d13fcfecc500d7cd2d9951bac/3a922a85701939624484e7f2fd07d32beed00d25/7e4cf2ec0ca236c3e5f904239cec6efe1f3baf22/ab46748bf98864f9c3f5559060bf8caf9df2b41e/87530b557affe01c764de32dbeb58cdf47234574/2283f79b22684d2812e5c76fc2280aae00390365 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2025-0861). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Debian Linux
• Google Cloud Platform
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• SolarWinds Security Event Manager
• Dell Secure Connect Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 4.4.243
• 4.9.243
• 4.14.206
• 4.19.157
• 5.4.0
• 5.4.1
• 5.4.2
• 5.4.3
• 5.4.4
• 5.4.5
• 5.4.6
• 5.4.7
• 5.4.8
• 5.4.9
• 5.4.10
• 5.4.11
• 5.4.12
• 5.4.13
• 5.4.14
• 5.4.15
• 5.4.16
• 5.4.17
• 5.4.18
• 5.4.19
• 5.4.20
• 5.4.21
• 5.4.22
• 5.4.23
• 5.4.24
• 5.4.25
• 5.4.26
• 5.4.27
• 5.4.28
• 5.4.29
• 5.4.30
• 5.4.31
• 5.4.32
• 5.4.33
• 5.4.34
• 5.4.35
• 5.4.36
• 5.4.37
• 5.4.38
• 5.4.39
• 5.4.40
• 5.4.41
• 5.4.42
• 5.4.43
• 5.4.44
• 5.4.45
• 5.4.46
• 5.4.47
• 5.4.48
• 5.4.49
• 5.4.50
• 5.4.51
• 5.4.52
• 5.4.53
• 5.4.54
• 5.4.55
• 5.4.56
• 5.4.57
• 5.4.58
• 5.4.59
• 5.4.60
• 5.4.61
• 5.4.62
• 5.4.63
• 5.4.64
• 5.4.65
• 5.4.66
• 5.4.67
• 5.4.68
• 5.4.69
• 5.4.70
• 5.4.71
• 5.4.72
• 5.4.73
• 5.4.74
• 5.4.75
• 5.4.76
• 5.4.77
• 5.9.0
• 5.9.1
• 5.9.2
• 5.9.3
• 5.9.4
• 5.9.5
• 5.9.6
• 5.9.7
• 5.9.8

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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