CVE-2026-97416 btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk()
A local attacker with low privileges can cause a kernel crash via null pointer dereference in btrfs balance operations when handling corrupted filesystem metadata.
- 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-2026-97416?
CVE-2026-97416 is a 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: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk()
[BUG] Running btrfs balance can trigger a null-ptr-deref before relocating a data chunk when metadata corruption leaves a chunk in the chunk tree without a corresponding block group in the in-memory cache:
KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f] RIP: 0010:btrfs_may_alloc_data_chunk+0x40/0x1c0 fs/btrfs/volumes.c:3601 Call Trace: __btrfs_balance fs/btrfs/volumes.c:4217 [inline] btrfs_balance+0x2516/0x42b0 fs/btrfs/volumes.c:4604 btrfs_ioctl_balance fs/btrfs/ioctl.c:3577 [inline] btrfs_ioctl+0x25cf/0x5b90 fs/btrfs/ioctl.c:5313 ...
[CAUSE] __btrfs_balance() iterates the on-disk chunk tree and passes the chunk logical bytenr to btrfs_may_alloc_data_chunk() before relocating a data chunk. That helper then queries the in-memory block group cache:
cache = btrfs_lookup_block_group(fs_info, chunk_offset); chunk_type = cache->flags; /* cache may be NULL */
A corrupt image can contain a chunk item whose matching block group item is missing, so no block group is ever inserted into the cache. In that case btrfs_lookup_block_group() returns NULL.
The code only guards this with ASSERT(cache), which becomes a no-op when CONFIG_BTRFS_ASSERT is disabled. The subsequent dereference of cache->flags therefore crashes the kernel.
[FIX] Add a NULL check after btrfs_lookup_block_group() in btrfs_may_alloc_data_chunk() and print and error message for clarity.
Which versions are affected by CVE-2026-97416?
How do I fix CVE-2026-97416?
Apply the vendor's patch.
Is CVE-2026-97416 being exploited?
There is no known exploitation of CVE-2026-97416 in the wild and no public exploit code.
Sources
Also known as AZL-103586, BELL-CVE-2026-97416, DEBIAN-CVE-2026-97416, GHSA-2886-j9mj-2v9x, UBUNTU-CVE-2026-97416.