CVE-2025-39884 btrfs: fix subvolume deletion lockup caused by inodes xarray race
A race condition in the Linux kernel btrfs filesystem can cause subvolume deletion lockups, leading to system denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39884?
CVE-2025-39884 is a medium-severity vulnerability in Linux kernel, published on 23 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix subvolume deletion lockup caused by inodes xarray race
There is a race condition between inode eviction and inode caching that can cause a live struct btrfs_inode to be missing from the root->inodes xarray. Specifically, there is a window during evict() between the inode being unhashed and deleted from the xarray. If btrfs_iget() is called for the same inode in that window, it will be recreated and inserted into the xarray, but then eviction will delete the new entry, leaving nothing in the xarray:
Thread 1 Thread 2 --------------------------------------------------------------- evict() remove_inode_hash() btrfs_iget_path() btrfs_iget_locked() btrfs_read_locked_inode() btrfs_add_inode_to_root() destroy_inode() btrfs_destroy_inode() btrfs_del_inode_from_root() __xa_erase
In turn, this can cause issues for subvolume deletion. Specifically, if an inode is in this lost state, and all other inodes are evicted, then btrfs_del_inode_from_root() will call btrfs_add_dead_root() prematurely. If the lost inode has a delayed_node attached to it, then when btrfs_clean_one_deleted_snapshot() calls btrfs_kill_all_delayed_nodes(), it will loop forever because the delayed_nodes xarray will never become empty (unless memory pressure forces the inode out). We saw this manifest as soft lockups in production.
Fix it by only deleting the xarray entry if it matches the given inode (using __xa_cmpxchg()).
Weakness: CWE-667
Which versions are affected by CVE-2025-39884?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39884?
Apply the vendor's patch.
Is CVE-2025-39884 being exploited?
There is no known exploitation of CVE-2025-39884 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39884, DEBIAN-CVE-2025-39884, GHSA-8f6j-f2h2-wfrj, ROOT-OS-UBUNTU-2204-CVE-2025-39884, ROOT-OS-UBUNTU-2404-CVE-2025-39884, UBUNTU-CVE-2025-39884.