CVE-2026-93798 btrfs: fix reloc root cleanup in merge_reloc_roots()
A race condition in the Linux kernel's Btrfs filesystem could lead to inconsistent state during relocation root cleanup, potentially causing stability issues.
- 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-2026-93798?
CVE-2026-93798 is a high-severity vulnerability in Linux, published on 24 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: fix reloc root cleanup in merge_reloc_roots()
If the root we got has zero root refs in its root item, we are resetting the root's ->reloc_root without using barriers like we do everywhere else. Sashiko complained about this while reviewing another patch, and it's correct (see the Link tag below).
Also, we should not clear BTRFS_ROOT_DEAD_RELOC_TREE from the root unless the root points to the reloc root we have.
Fix this by using clear_reloc_root(), which issues the memory barrier after setting the root's ->reloc_root to NULL and before clearing the bit BTRFS_ROOT_DEAD_RELOC_TREE from the root.
Which versions are affected by CVE-2026-93798?
How do I fix CVE-2026-93798?
Apply the vendor's patch.
Is CVE-2026-93798 being exploited?
There is no known exploitation of CVE-2026-93798 in the wild and no public exploit code.
Sources
Also known as AZL-103637, BELL-CVE-2026-93798, DEBIAN-CVE-2026-93798, GHSA-9c2v-whhq-6g24, UBUNTU-CVE-2026-93798.