CVE-2021-47189: btrfs: fix memory ordering between normal and ordered work functions
First published: Wed Apr 10 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix memory ordering between normal and ordered work functions Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever. This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to: pc : submit_compressed_extents+0x38/0x3d0 lr : async_cow_submit+0x50/0xd0 sp : ffff800015d4bc20 <registers omitted for brevity> Call trace: submit_compressed_extents+0x38/0x3d0 async_cow_submit+0x50/0xd0 run_ordered_work+0xc8/0x280 btrfs_work_helper+0x98/0x250 process_one_work+0x1f0/0x4ac worker_thread+0x188/0x504 kthread+0x110/0x114 ret_from_fork+0x10/0x18 Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Red Hat Kernel-devel | ||
| Linux Kernel | >=3.15<4.4.293 | |
| Linux Kernel | >=4.5<4.9.291 | |
| Linux Kernel | >=4.10<4.14.256 | |
| Linux Kernel | >=4.15<4.19.218 | |
| Linux Kernel | >=4.20<5.4.162 | |
| Linux Kernel | >=5.5<5.10.82 | |
| Linux Kernel | >=5.11<5.15.5 | |
| Linux Kernel | =5.16-rc1 |
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Reference Links
- https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779
- https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500
- https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136
- https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513
- https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179
- https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987
- https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff
- https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9
Frequently Asked Questions
What is the severity of CVE-2021-47189?
CVE-2021-47189 has been classified as a medium severity vulnerability in the Linux kernel.
How do I fix CVE-2021-47189?
To fix CVE-2021-47189, you should update the Linux kernel to the latest version that includes the patch.
What is the impact of CVE-2021-47189?
CVE-2021-47189 can potentially lead to unexpected behavior in memory ordering between normal and ordered work functions.
Which versions of the Linux kernel are affected by CVE-2021-47189?
CVE-2021-47189 affects various versions of the Linux kernel prior to its fix and may vary based on distribution.
Is CVE-2021-47189 exploitable remotely?
CVE-2021-47189 is primarily focused on kernel functions, making remote exploitation unlikely but potential risks may exist depending on the specific context of use.
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