CVE-2026-89645 btrfs: drop recovered reloc root refs on recovery failure
A reference counting error in the Linux kernel's Btrfs filesystem can cause memory leaks and potential instability during relocation recovery failures.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89645?
CVE-2026-89645 is a memory corruption vulnerability in Linux, published on 11 Sep 2026. 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: drop recovered reloc root refs on recovery failure
During relocation recovery, each fs root gets a reference to its relocation root. If loading or adding a later root fails, or if the first transaction commit fails, btrfs_recover_relocation() jumps to out_unset before merge_reloc_roots() and clean_dirty_subvols().
put_reloc_control() drops the list-owned relocation root references, but it does not clear fs_root->reloc_root or drop the references owned by those pointers. Mount cleanup only drops them when BTRFS_FS_ERROR is set, so an error such as -ENOMEM while processing a later root can leave references behind.
Keep temporary references to the fs roots associated during recovery. On failure, clear their reloc_root pointers and drop the corresponding references. Once the first transaction commit succeeds, drop only the temporary fs root references and let the normal merge and cleanup paths handle the relocation roots.
Fault injection on a pending-relocation image confirmed the cleanup gap. With an injected first-commit failure, 25 fs roots had reloc_root set with fs_error=0. With this fix, the same failure path drops that count to 0 before mount fails.
Which versions are affected by CVE-2026-89645?
How do I fix CVE-2026-89645?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89645 being exploited?
There is no known exploitation of CVE-2026-89645 in the wild and no public exploit code.
Sources
Also known as AZL-100844, BELL-CVE-2026-89645, DEBIAN-CVE-2026-89645, GHSA-m8pq-6746-5gfc, UBUNTU-CVE-2026-89645.