Linux Kernel up to 5.12.9 sch_htb null pointer dereference

Summaryinfo

A vulnerability identified as problematic has been detected in Linux Kernel up to 5.12.9. This vulnerability affects unknown code of the component sch_htb. Performing a manipulation results in null pointer dereference. This vulnerability is reported as CVE-2021-47125. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Linux Kernel up to 5.12.9. This affects some unknown functionality of the component sch_htb. The manipulation with an unknown input leads to a null pointer dereference vulnerability. CWE is classifying the issue as CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. This is going to have an impact on availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: sch_htb: fix refcount leak in htb_parent_to_leaf_offload The commit ae81feb7338c ("sch_htb: fix null pointer dereference on a null new_q") fixes a NULL pointer dereference bug, but it is not correct. Because htb_graft_helper properly handles the case when new_q is NULL, and after the previous patch by skipping this call which creates an inconsistency : dev_queue->qdisc will still point to the old qdisc, but cl->parent->leaf.q will point to the new one (which will be noop_qdisc, because new_q was NULL). The code is based on an assumption that these two pointers are the same, so it can lead to refcount leaks. The correct fix is to add a NULL pointer check to protect qdisc_refcount_inc inside htb_parent_to_leaf_offload.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2021-47125 since 03/04/2024. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 5.12.10 or 5.13 eliminates this vulnerability. Applying the patch 2411c02d0389/944d671d5faa 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.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.12.0
• 5.12.1
• 5.12.2
• 5.12.3
• 5.12.4
• 5.12.5
• 5.12.6
• 5.12.7
• 5.12.8
• 5.12.9

License

• open-source

Website

• Vendor: https://www.kernel.org/

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