UBUNTU-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.
02 / AFFECTED SOFTWARE
Affected packages
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/44f52bbe96dfdbe4aca3818a2534520082a07040
- https://git.kernel.org/stable/c/44f52bbe96dfdbe4aca3818a2534520082a07040
- 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://git.kernel.org/stable/c/c3a403d8ce36f5a809a492581de5ad17843e4701
- https://ubuntu.com/security/CVE-2024-56759
- https://ubuntu.com/security/notices/USN-7379-1
- https://ubuntu.com/security/notices/USN-7379-2
- https://ubuntu.com/security/notices/USN-7380-1
- https://ubuntu.com/security/notices/USN-7381-1
- https://ubuntu.com/security/notices/USN-7382-1
- https://ubuntu.com/security/notices/USN-7387-1
- https://ubuntu.com/security/notices/USN-7387-2
- https://ubuntu.com/security/notices/USN-7387-3
- https://ubuntu.com/security/notices/USN-7388-1
- https://ubuntu.com/security/notices/USN-7389-1
- https://ubuntu.com/security/notices/USN-7390-1
- https://ubuntu.com/security/notices/USN-7407-1
- https://ubuntu.com/security/notices/USN-7421-1
- https://ubuntu.com/security/notices/USN-7458-1
- https://ubuntu.com/security/notices/USN-7459-1
- https://ubuntu.com/security/notices/USN-7459-2
- https://ubuntu.com/security/notices/USN-7513-1
- https://ubuntu.com/security/notices/USN-7513-2
- https://ubuntu.com/security/notices/USN-7513-3
- https://ubuntu.com/security/notices/USN-7513-4
- https://ubuntu.com/security/notices/USN-7513-5
- https://ubuntu.com/security/notices/USN-7514-1
- https://ubuntu.com/security/notices/USN-7515-1
- https://ubuntu.com/security/notices/USN-7515-2
- https://ubuntu.com/security/notices/USN-7522-1
- https://ubuntu.com/security/notices/USN-7523-1
- https://ubuntu.com/security/notices/USN-7524-1
- https://www.cve.org/CVERecord?id=CVE-2024-56759