{"id":"CVE-2025-37856","title":"btrfs: harden block_group::bg_list against list_del() races","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: harden block_group::bg_list against list_del() races\n\nAs far as I can tell, these calls of list_del_init() on bg_list cannot\nrun concurrently with btrfs_mark_bg_…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 9039afe6240ae01d6caf2fa731590ac74fb8a69b","Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < bf089c4d1141b27332c092b1dcca5022c415a3b6","Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 909e60fb469d4101c6b08cf6e622efb062bb24a1","Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 185fd73e5ac06027c4be9a129e59193f6a3ef202","Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 7511e29cf1355b2c47d0effb39e463119913e2f6","Linux edf3b5aadb2515c808200b904baa5b70a727f0ac","Linux 01eca70ef8cf499d0cb6d1bbd691558e7792cf17","Linux 5d19abcffd8404078dfa7d7118cec357b5e7bc58","Linux >= 5.15.128 < 5.16","Linux >= 6.1.47 < 6.2","Linux >= 6.4.12 < 6.5","Linux 6.5"],"published":"2025-05-09","updated":"2026-10-21","sourceUpdated":"2026-10-21T12:36:30.528Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-37856","references":[{"url":"https://git.kernel.org/stable/c/9039afe6240ae01d6caf2fa731590ac74fb8a69b"},{"url":"https://git.kernel.org/stable/c/bf089c4d1141b27332c092b1dcca5022c415a3b6"},{"url":"https://git.kernel.org/stable/c/909e60fb469d4101c6b08cf6e622efb062bb24a1"},{"url":"https://git.kernel.org/stable/c/185fd73e5ac06027c4be9a129e59193f6a3ef202"},{"url":"https://git.kernel.org/stable/c/7511e29cf1355b2c47d0effb39e463119913e2f6"}],"tags":["cve.org"],"epss":0.00308,"epssPercentile":0.2352,"ingestedAt":"2026-10-21T12:48:53.711Z","slug":"CVE-2025-37856","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: harden block_group::bg_list against list_del() races\n\nAs far as I can tell, these calls of list_del_init() on bg_list cannot\nrun concurrently with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(),\nas they are in transaction error paths and situations where the block\ngroup is readonly.\n\nHowever, if there is any chance at all of racing with mark_bg_unused(),\nor a different future user of bg_list, better to be safe than sorry.\n\nOtherwise we risk the following interleaving (bg_list refcount in parens)\n\nT1 (some random op)                       T2 (btrfs_mark_bg_unused)\n                                        !list_empty(&bg->bg_list); (1)\nlist_del_init(&bg->bg_list); (1)\n                                        list_move_tail (1)\nbtrfs_put_block_group (0)\n                                        btrfs_delete_unused_bgs\n                                             bg = list_first_entry\n                                             list_del_init(&bg->bg_list);\n                                             btrfs_put_block_group(bg); (-1)\n\nUltimately, this results in a broken ref count that hits zero one deref\nearly and the real final deref underflows the refcount, resulting in a WARNING.\n\n## Affected\n\n- `Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 9039afe6240ae01d6caf2fa731590ac74fb8a69b`\n- `Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < bf089c4d1141b27332c092b1dcca5022c415a3b6`\n- `Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 909e60fb469d4101c6b08cf6e622efb062bb24a1`\n- `Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 185fd73e5ac06027c4be9a129e59193f6a3ef202`\n- `Linux >= a9f189716cf15913c453299d72f69c51a9b0f86b < 7511e29cf1355b2c47d0effb39e463119913e2f6`\n- `Linux edf3b5aadb2515c808200b904baa5b70a727f0ac`\n- `Linux 01eca70ef8cf499d0cb6d1bbd691558e7792cf17`\n- `Linux 5d19abcffd8404078dfa7d7118cec357b5e7bc58`\n- `Linux >= 5.15.128 < 5.16`\n- `Linux >= 6.1.47 < 6.2`\n- `Linux >= 6.4.12 < 6.5`\n- `Linux 6.5`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}