CVE-2023-4208

A use-after-free vulnerability in the Linux kernels net/sched: cls_u32 component can be exploited to achieve local privilege escalation.

When u32_change() is called on an existing filter, the whole tcf_result struct is always copied into the new instance of the filter. This causes a problem when updating a filter bound to a class, as tcf_unbind_filter() is always called on the old instance in the success path, decreasing filter_cnt of the still referenced class and allowing it to be deleted, leading to a use-after-free.

We recommend upgrading past commit 3044b16e7c6fe5d24b1cdbcf1bd0a9d92d1ebd81.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3044b16e7c6fe5d24b1cdbcf1bd0a9d92d1ebd81
• https://kernel.dance/3044b16e7c6fe5d24b1cdbcf1bd0a9d92d1ebd81
• https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html
• https://www.debian.org/security/2023/dsa-5492
• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3044b16e7c6fe5d24b1cdbcf1bd0a9d92d1ebd81
• https://kernel.dance/3044b16e7c6fe5d24b1cdbcf1bd0a9d92d1ebd81
• https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html
• https://www.debian.org/security/2023/dsa-5492