CVE-2025-37856
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk18th percentile - higher than 18% of all known CVEs
Summary
In the Linux kernel's Btrfs filesystem, list_del_init() operations on the bg_list of block groups can race with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(), leading to double reference decrement and a kernel warning.
Risk Assessment
A race condition can corrupt the block group reference count, causing premature memory release and potential system crash.
Recommendation
Apply the Linux kernel patch that protects the bg_list from races with proper locking.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: btrfs: harden block_group::bg_list against list_del() races As far as I can tell, these calls of list_del_init() on bg_list cannot run concurrently with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(), as they are in transaction error paths and situations where the block group is readonly. However, if there is any chance at all of racing with mark_bg_unused(), or a different future user of bg_list, better to be safe than sorry. Otherwise we risk the following interleaving (bg_list refcount in parens) T1 (some random op) T2 (btrfs_mark_bg_unused) !list_empty(&bg->bg_list); (1) list_del_init(&bg->bg_list); (1) list_move_tail (1) btrfs_put_block_group (0) btrfs_delete_unused_bgs bg = list_first_entry list_del_init(&bg->bg_list); btrfs_put_block_group(bg); (-1) Ultimately, this results in a broken ref count that hits zero one deref early and the real final deref underflows the refcount, resulting in a WARNING.

