CVE-2026-97416

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.