mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-07-22 02:17:36 -04:00
Code Issues Packages Projects Releases Wiki Activity

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

Browse Source 
[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.

Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
ZhengYuan Huang
2026-03-25 08:43:38 +08:00
committed by David Sterba
parent 7a308f6d29
commit 18d32b0013
1 changed files with 5 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
fs/btrfs/volumes.c
View File

@@ -3718,7 +3718,11 @@ static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info,
u64 chunk_type;
cache = btrfs_lookup_block_group(fs_info, chunk_offset);
ASSERT(cache);
if (unlikely(!cache)) {
btrfs_err(fs_info, "balance: chunk at bytenr %llu has no corresponding block group",
chunk_offset);
return -EUCLEAN;
}
chunk_type = cache->flags;
btrfs_put_block_group(cache);