CVE-2021-47189

MEDIUM
Published Apr 10, 2024 Modified Apr 30, 2025

Description

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.

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CVSS v3.1 Score

6.3
MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9 https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500 https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179 https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987 https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136 https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779 https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513 https://git.kernel.org/stable/c/45da9c1767ac31857df572f0a909fbe88fd5a7e9 https://git.kernel.org/stable/c/47e6f9f69153247109042010f3a77579e9dc61ff https://git.kernel.org/stable/c/637d652d351fd4f263ef302dc52f3971d314e500 https://git.kernel.org/stable/c/670f6b3867c8f0f11e5097f353b164cecfec6179 https://git.kernel.org/stable/c/6adbc07ebcaf8bead08b21687d49e0fc94400987 https://git.kernel.org/stable/c/804a9d239ae9cbe88e861a7cd62319cc6ec7b136 https://git.kernel.org/stable/c/bd660a20fea3ec60a49709ef5360f145ec0fe779 https://git.kernel.org/stable/c/ed058d735a70f4b063323f1a7bb33cda0f987513

Frequently Asked Questions

What is CVE-2021-47189? +
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. It has a CVSS v3.1 base score of 6.3 (MEDIUM).
How severe is CVE-2021-47189? +
CVE-2021-47189 has a CVSS v3.1 score of 6.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2021-47189? +
CVE-2021-47189 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-2021-47189? +
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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