CVE-2021-46989

MEDIUM
Published Feb 28, 2024 Modified Mar 14, 2025

Description

In the Linux kernel, the following vulnerability has been resolved: hfsplus: prevent corruption in shrinking truncate I believe there are some issues introduced by commit 31651c607151 ("hfsplus: avoid deadlock on file truncation") HFS+ has extent records which always contains 8 extents. In case the first extent record in catalog file gets full, new ones are allocated from extents overflow file. In case shrinking truncate happens to middle of an extent record which locates in extents overflow file, the logic in hfsplus_file_truncate() was changed so that call to hfs_brec_remove() is not guarded any more. Right action would be just freeing the extents that exceed the new size inside extent record by calling hfsplus_free_extents(), and then check if the whole extent record should be removed. However since the guard (blk_cnt > start) is now after the call to hfs_brec_remove(), this has unfortunate effect that the last matching extent record is removed unconditionally. To reproduce this issue, create a file which has at least 10 extents, and then perform shrinking truncate into middle of the last extent record, so that the number of remaining extents is not under or divisible by 8. This causes the last extent record (8 extents) to be removed totally instead of truncating into middle of it. Thus this causes corruption, and lost data. Fix for this is simply checking if the new truncated end is below the start of this extent record, making it safe to remove the full extent record. However call to hfs_brec_remove() can't be moved to it's previous place since we're dropping ->tree_lock and it can cause a race condition and the cached info being invalidated possibly corrupting the node data. Another issue is related to this one. When entering into the block (blk_cnt > start) we are not holding the ->tree_lock. We break out from the loop not holding the lock, but hfs_find_exit() does unlock it. Not sure if it's possible for someone else to take the lock under our feet, but it can cause hard to debug errors and premature unlocking. Even if there's no real risk of it, the locking should still always be kept in balance. Thus taking the lock now just before the check.

Is your site exposed to CVE-2021-46989?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected Products

Vendor Product
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/52dde855663e5db824af51db39b5757d2ef3e28a https://git.kernel.org/stable/c/97314e45aa1223a42d60256a62c5d9af54baf446 https://git.kernel.org/stable/c/adbd8a2a8cc05d9e501f93e5c95c59307874cc99 https://git.kernel.org/stable/c/c3187cf32216313fb316084efac4dab3a8459b1d https://git.kernel.org/stable/c/c451a6bafb5f422197d31536f82116aed132b72c https://git.kernel.org/stable/c/c477f62db1a0c0ecaa60a29713006ceeeb04b685 https://git.kernel.org/stable/c/52dde855663e5db824af51db39b5757d2ef3e28a https://git.kernel.org/stable/c/97314e45aa1223a42d60256a62c5d9af54baf446 https://git.kernel.org/stable/c/adbd8a2a8cc05d9e501f93e5c95c59307874cc99 https://git.kernel.org/stable/c/c3187cf32216313fb316084efac4dab3a8459b1d https://git.kernel.org/stable/c/c451a6bafb5f422197d31536f82116aed132b72c https://git.kernel.org/stable/c/c477f62db1a0c0ecaa60a29713006ceeeb04b685

Frequently Asked Questions

What is CVE-2021-46989? +
In the Linux kernel, the following vulnerability has been resolved: hfsplus: prevent corruption in shrinking truncate I believe there are some issues introduced by commit 31651c607151 ("hfsplus: avoid deadlock on file truncation") HFS+ has extent records which always contains 8 extents. In case the first extent record in catalog file gets full, new ones are allocated from extents overflow file. In case shrinking truncate happens to middle of an extent record which locates in extents overflow file, the logic in hfsplus_file_truncate() was changed so that call to hfs_brec_remove() is not guarded any more. Right action would be just freeing the extents that exceed the new size inside extent record by calling hfsplus_free_extents(), and then check if the whole extent record should be removed. However since the guard (blk_cnt > start) is now after the call to hfs_brec_remove(), this has unfortunate effect that the last matching extent record is removed unconditionally. To reproduce this issue, create a file which has at least 10 extents, and then perform shrinking truncate into middle of the last extent record, so that the number of remaining extents is not under or divisible by 8. This causes the last extent record (8 extents) to be removed totally instead of truncating into middle of it. Thus this causes corruption, and lost data. Fix for this is simply checking if the new truncated end is below the start of this extent record, making it safe to remove the full extent record. However call to hfs_brec_remove() can't be moved to it's previous place since we're dropping ->tree_lock and it can cause a race condition and the cached info being invalidated possibly corrupting the node data. Another issue is related to this one. When entering into the block (blk_cnt > start) we are not holding the ->tree_lock. We break out from the loop not holding the lock, but hfs_find_exit() does unlock it. Not sure if it's possible for someone else to take the lock under our feet, but it can cause hard to debug errors and premature unlocking. Even if there's no real risk of it, the locking should still always be kept in balance. Thus taking the lock now just before the check. It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2021-46989? +
CVE-2021-46989 has a CVSS v3.1 score of 5.5 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-2021-46989? +
CVE-2021-46989 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-2021-46989? +
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.

Related Vulnerabilities

CVE-2025-9588 10.0

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') vulnerability in Iron Mountain Archiving Services Inc. …
CVE-2025-57870 10.0

A SQL Injection vulnerability exists in Esri ArcGIS Server versions 11.3, 11.4 and 11.5 on Windows, Linux and Kubernetes. This …
CVE-2026-48286 10.0

Adobe Campaign Classic (ACC) versions 7.4.3 build 9396 and earlier are affected by an Incorrect Authorization vulnerability that could result …
CVE-2026-13782 10.0

Use after free in Browser in Google Chrome prior to 150.0.7871.47 allowed a remote attacker who had compromised the renderer …
CVE-2026-48449 10.0

Adobe Campaign Classic (ACC) is affected by an Incorrect Authorization vulnerability that could result in arbitrary code execution in the …
CVE-2026-48303 10.0

Adobe Campaign Classic (ACC) versions 7.4.3 build 9394 and earlier are affected by an Incorrect Authorization vulnerability that could result …

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2021-46989 — free, no signup required.