CVE-2024-56759: linux kernel Use-After-Free — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free when COWing tree bock and tracing is enabled When a COWing a tree block, at btrfs_cow_block(), and we have the tracepoint trace_btrfs_cow_block() enabled and preemption is also enabled (CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent buffer while inside the tracepoint code. This is because in some paths that call btrfs_cow_block(), such as btrfs_search_slot(), we are holding the last reference on the extent buffer @buf so btrfs_force_cow_block() drops the last reference on the @buf extent buffer when it calls free_extent_buffer_stale(buf), which schedules the release of the extent buffer with RCU. This means that if we are on a kernel with preemption, the current task may be preempted before calling trace_btrfs_cow_block() and the extent buffer already released by the time trace_btrfs_cow_block() is called, resulting in a use-after-free. Fix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to btrfs_force_cow_block() before the COWed extent buffer is freed. This also has a side effect of invoking the tracepoint in the tree defrag code, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is called there, but this is fine and it was actually missing there.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
linux	linux_kernel	< 6.12.8
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/44f52bbe96dfdbe4aca3818a2534520082a07040 https://git.kernel.org/stable/c/c3a403d8ce36f5a809a492581de5ad17843e4701

Other References

https://git.kernel.org/stable/c/526ff5b27f090fb15040471f892cd2c9899ce314 https://git.kernel.org/stable/c/66376f1a73cba57fd0af2631d7888605b738e499 https://git.kernel.org/stable/c/9a466b8693b9add05de99af00c7bdff8259ecf19 https://git.kernel.org/stable/c/ba5120a2fb5f23b4d39d302e181aa5d4e28a90d1 https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html

Frequently Asked Questions

What is CVE-2024-56759? +

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free when COWing tree bock and tracing is enabled When a COWing a tree block, at btrfs_cow_block(), and we have the tracepoint trace_btrfs_cow_block() enabled and preemption is also enabled (CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent buffer while inside the tracepoint code. This is because in some paths that call btrfs_cow_block(), such as btrfs_search_slot(), we are holding the last reference on the extent buffer @buf so btrfs_force_cow_block() drops the last reference on the @buf extent buffer when it calls free_extent_buffer_stale(buf), which schedules the release of the extent buffer with RCU. This means that if we are on a kernel with preemption, the current task may be preempted before calling trace_btrfs_cow_block() and the extent buffer already released by the time trace_btrfs_cow_block() is called, resulting in a use-after-free. Fix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to btrfs_force_cow_block() before the COWed extent buffer is freed. This also has a side effect of invoking the tracepoint in the tree defrag code, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is called there, but this is fine and it was actually missing there. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2024-56759? +

CVE-2024-56759 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2024-56759? +

CVE-2024-56759 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2024-56759? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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