Improper Locking Affecting kernel-tools-debuginfo package, versions <0:4.14.301-224.520.amzn2
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Test your applications- Snyk IDSNYK-AMZN2-KERNELTOOLSDEBUGINFO-10499988
- published25 Jun 2025
- disclosed1 May 2025
Introduced: 1 May 2025
CVE-2022-49850 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2 kernel-tools-debuginfo to version 0:4.14.301-224.520.amzn2 or higher.
This issue was patched in ALAS2-2022-1903.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-tools-debuginfo package and not the kernel-tools-debuginfo package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix deadlock in nilfs_count_free_blocks()
A semaphore deadlock can occur if nilfs_get_block() detects metadata corruption while locating data blocks and a superblock writeback occurs at the same time:
task 1 task 2
- A file operation *
nilfs_truncate()
nilfs_get_block()
down_read(rwsem A) <--
nilfs_bmap_lookup_contig()
... generic_shutdown_super()
nilfs_put_super()
* Prepare to write superblock *
down_write(rwsem B) <--
nilfs_cleanup_super()
* Detect b-tree corruption * nilfs_set_log_cursor()
nilfs_bmap_convert_error() nilfs_count_free_blocks()
__nilfs_error() down_read(rwsem A) <--
nilfs_set_error()
down_write(rwsem B) <--
*** DEADLOCK ***</li>
Here, nilfs_get_block() readlocks rwsem A (= NILFS_MDT(dat_inode)->mi_sem) and then calls nilfs_bmap_lookup_contig(), but if it fails due to metadata corruption, __nilfs_error() is called from nilfs_bmap_convert_error() inside the lock section.
Since __nilfs_error() calls nilfs_set_error() unless the filesystem is read-only and nilfs_set_error() attempts to writelock rwsem B (= nilfs->ns_sem) to write back superblock exclusively, hierarchical lock acquisition occurs in the order rwsem A -> rwsem B.
Now, if another task starts updating the superblock, it may writelock rwsem B during the lock sequence above, and can deadlock trying to readlock rwsem A in nilfs_count_free_blocks().
However, there is actually no need to take rwsem A in nilfs_count_free_blocks() because it, within the lock section, only reads a single integer data on a shared struct with nilfs_sufile_get_ncleansegs(). This has been the case after commit aa474a220180 ("nilfs2: add local variable to cache the number of clean segments"), that is, even before this bug was introduced.
So, this resolves the deadlock problem by just not taking the semaphore in nilfs_count_free_blocks().
References
- http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-49850
- https://git.kernel.org/stable/c/1d4ff73062096c21b47954d2996b4df259777bda
- https://git.kernel.org/stable/c/36ff974b0310771417c0be64b64aa221bd70d63d
- https://git.kernel.org/stable/c/3c89ca6d3dfa6c09c515807a7a97a521f5d5147e
- https://git.kernel.org/stable/c/8ac932a4921a96ca52f61935dbba64ea87bbd5dc
- https://git.kernel.org/stable/c/8b4506cff6630bb474bb46a2a75c31e533a756ba
- https://git.kernel.org/stable/c/abc082aac0d9b6b926038fc3adb7008306581be2
- https://git.kernel.org/stable/c/cb029b54953420f7a2d65100f1c5107f14411bdc
- https://git.kernel.org/stable/c/f0cc93080d4c09510b74ecba87fd778cca390bb1