btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-97416
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-24 17:17:19 UTC
Updated2026-09-25 13:17:25 UTC
DescriptionIn 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.

Risk And Classification

EPSS: 0.001660000 probability, percentile 0.052110000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected a6f93c71d412ba8ed743152c3a54ad0b78dcd9c7 9740dd0c17a4be8cc47a06c5ca5293471a7e286e git Not specified
CNA Linux Linux affected a6f93c71d412ba8ed743152c3a54ad0b78dcd9c7 59f75e0c8724d4adebc08c7dd3ff2358b80c21f7 git Not specified
CNA Linux Linux affected a6f93c71d412ba8ed743152c3a54ad0b78dcd9c7 18d32b0013efba19f7ad3e5b08d7aee813d604a6 git Not specified
CNA Linux Linux affected 4.16 Not specified
CNA Linux Linux unaffected 4.16 semver Not specified
CNA Linux Linux unaffected 6.12.111 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.53 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9740dd0c17a4be8cc47a06c5ca5293471a7e286e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/18d32b0013efba19f7ad3e5b08d7aee813d604a6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/59f75e0c8724d4adebc08c7dd3ff2358b80c21f7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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