Overview
About vulnerability
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.
Details
- Affected product:
- AlmaLinux 9.2 ESU , Amazon Linux 2 ELS , CentOS 6 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 6 ELS , CloudLinux 7 ELS , Debian 10 ELS , Oracle Linux 6 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , TuxCare 9.6 ESU , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS , Ubuntu 20.04 ELS
- Affected packages:
- kernel-uek @ 5.4.17 (+22 more)
Fixes
KernelCare state
Live-patch status from KernelCare for each operating system.
| Operating system | Status | Covered kernels |
|---|---|---|
| Amazon Linux 2023 | Planned | — |
| Amazon Linux 2 5.10 | Will Not Fix | — |
| CentOS 7 ELS | Released |
12 kernels
|
| Debian 11 | Released |
33 kernels
|
| Debian 11 cloud | Released |
13 kernels
|
| Debian 12 | Released |
20 kernels
|
| Oracle Linux 8 UEK 7 | Released |
53 kernels
|
| Oracle Linux 9 UEK 7 | Released |
53 kernels
|
| Proxmox VE 7 5.15 | Released |
47 kernels
|
| Ubuntu 20.04 HWE AWS | Released |
52 kernels
|
| Ubuntu 20.04 HWE Azure | Released |
36 kernels
|
| Ubuntu 22.04 | Released |
69 kernels
|
| Ubuntu 22.04 AWS | Released |
60 kernels
|
| Ubuntu 22.04 Azure | Released |
56 kernels
|
| Ubuntu 24.04 | Released |
22 kernels
|
| Ubuntu 24.04 AWS | Ready For Release | — |