Linux Kernel up to 7.2.5 btrfs btree_writepages deadlock

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.5. It has been classified as critical. The affected element is the function btree_writepages of the component btrfs. The manipulation leads to deadlock. This vulnerability is referenced as CVE-2026-90261. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 7.2.5. This issue affects the function btree_writepages of the component btrfs. The manipulation with an unknown input leads to a deadlock vulnerability. Using CWE to declare the problem leads to CWE-833. The product contains multiple threads or executable segments that are waiting for each other to release a necessary lock, resulting in deadlock. Impacted is availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: btrfs: zoned: flush active metadata block group at btree_writepages() start btree_writepages() writes the btree inode's dirty metadata in ascending logical address order. On a zoned filesystem only one metadata and one system block group is active for writing at a time, and check_bg_is_active() (via btrfs_check_meta_write_pointer()) pivots the active block group as writeback moves from one block group to the next. If the active block group sits at a higher logical address than another block group that also holds dirty metadata, the ascending walk reaches the lower one first and, to write it, has to finish the active block group and activate the lower one. It cannot finish a block group that still has unsent IO, and during WB_SYNC_ALL && !for_sync (commit) writeback it deliberately refuses to wait for that IO under fs_info->zoned_meta_io_lock, as that can deadlock. The pivot thus cannot issue the submission itself either, so it gives up: btrfs_check_meta_write_pointer() returns -EAGAIN, which btrfs_write_and_wait_transaction() treats as fatal and aborts the transaction, forcing the filesystem read-only. This happens intermittently under metadata-heavy relocation (e.g. fstests btrfs/187). Flush the active metadata and system block groups at the start of btree_writepages(), under the fs_info->zoned_meta_io_lock it already holds, so they have no unsent IO left and the later pivot can finish them and make forward progress.

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2026-90261 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/17/2026). The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 7.2.6 or 7.3-rc1 eliminates this vulnerability. Applying the patch e2de2989adb3e58c2320e57c255f52e065667b5e/ecc05eda9a346848ae01a6c8bfa3f0bec133bd8b is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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