{"id":"CVE-2026-93800","revision":"56e35f5bc2b64957a6224e39ea64b9b8","records":[{"revision":"56e35f5bc2b64957a6224e39ea64b9b8","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-93800","aliases":[],"title":"btrfs: fix use-after-free on reloc root after error in insert_dirty_subvol()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix use-after-free on reloc root after error in insert_dirty_subvol()\n\nIf during relocation we fail in insert_dirty_subvol() because\nbtrfs_update_reloc_root() returned an error, we will leave a root's\nreloc_root field pointing to a reloc root that was freed instead of NULL,\nresulting later in a use-after-free, or double free attempt during\nunmount.\n\nThe sequence of steps is this:\n\n1) During relocation the call to btrfs_update_reloc_root() in\n insert_dirty_subvol() fails, so insert_dirty_subvol() returns the\n error to merge_reloc_root() without adding the root to the list\n rc->dirty_subvol_roots;\n\n2) Then merge_reloc_root() aborts the current transaction because\n insert_dirty_subvol() returned an error;\n\n3) Up the call chain, merge_reloc_roots() gets the error, adds the\n reloc root for root X to the local reloc_roots list and jumps to the\n 'out' label, where it calls free_reloc_roots() to free all the reloc\n roots in the local reloc_roots list. This frees the reloc root for\n root X;\n\n4) We go up the call chain to relocate_block_group() which calls\n clean_dirty_subvols() to go over dirty roots and set their\n ->reloc_root field to NULL, but root X is not in the dirty_subvol_roots\n list, so its ->reloc_root still points to a reloc root;\n\n5) Relocation finishes, with an error and a transaction abort, but the\n ->reloc_root field for root X still points to the reloc root that was\n freed in step 3;\n\n6) When unmounting the fs we end up calling:\n\n btrfs_free_fs_roots()\n btrfs_drop_and_free_fs_root()\n --> calls btrfs_put_root() against root X's ->reloc_root\n which is not NULL and points to the already freed\n reloc root in step 4 above\n\n Resulting in a use-after-free to a double free attempt.\n\nSyzbot reported this with the following dmesg/syslog:\n\n [ 106.004389][ T5339] BTRFS error (device loop0 state A): Transaction aborted (error -5)\n [ 106.014266][ T5339] BTRFS: error (device loop0 state A) in merge_reloc_root:1655: errno=-5 IO failure\n [ 106.021891][ T1061] BTRFS error (device loop0 state A): error while writing out transaction: -5\n [ 106.026964][ T1061] BTRFS warning (device loop0 state A): Skipping commit of aborted transaction.\n [ 106.033807][ T5340] BTRFS error (device loop0 state A): bdev /dev/loop0 errs: wr 3, rd 0, flush 0, corrupt 0, gen 0\n [ 106.039265][ T1061] BTRFS: error (device loop0 state A) in cleanup_transaction:2067: errno=-5 IO failure\n [ 106.044382][ T5339] BTRFS info (device loop0 state EA): forced readonly\n [ 106.074329][ T5339] BTRFS: error (device loop0 state EA) in merge_reloc_roots:1887: errno=-5 IO failure\n [ 106.081004][ T5356] BTRFS info (device loop0 state EA): scrub: started on devid 1\n [ 106.085611][ T5339] BTRFS info (device loop0 state EA): balance: ended with status: -30\n [ 106.089517][ T5356] BTRFS info (device loop0 state EA): scrub: not finished on devid 1 with status: -30\n [ 106.662365][ T5338] BTRFS info (device loop0 state EA): last unmount of filesystem 3a375e4e-b156-4d76-a2ad-16e198ce1409\n [ 106.682946][ T5338] ==================================================================\n [ 106.686574][ T5338] BUG: KASAN: slab-use-after-free in btrfs_put_root+0x2f/0x250\n [ 106.690090][ T5338] Write of size 4 at addr ffff88803f978630 by task syz.0.0/5338\n [ 106.693173][ T5338]\n [ 106.694279][ T5338] CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)\n [ 106.694293][ T5338] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\n [ 106.694300][ T5338] Call Trace:\n [ 106.694308][ T5338] \n [ 106.694314][ T5338] dump_stack_lvl+0xe8/0x150\n [ 106.694331][ T5338] print_address_description+0x55/0x1e0\n [ 106.694343][ T5338] ? btrfs_put_root+0x2f/0x250\n [ 106.694358][ T5338] print_report+0x58/0x70\n [ 106.\n---truncated---","state":0,"publishedAt":"2026-09-24T16:02:34.37+00:00","modifiedAt":"2026-10-03T10:57:34.733+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/btrfs/relocation.c\"\n ],\n \"versions\": [\n {\n \"version\": \"f32b84d7c977e1906a4781b93b3c93090b6cd675\",\n \"lessThan\": \"5a247097c5f94b51ffc991b444d998ad6e85875f\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"6372dd394ea907cd85a7a8063db320ec73dfaed0\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"9f599d120b2b79d2d937c3935b7cdf2697514283\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"a01837ae174a2a968c245a30e6dd010f50eaf05d\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"97a540d72ebcb21853d11f2a56782fe377f358e7\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"fda1b6636ff1846f00643e791099db5564b547d9\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"592fbcd50c99b8adf999a2a54f9245caff333139\",\n \"lessThan\": \"83201804efa4a5168be754e1dfc9b2faee760cac\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"aa18bc1ff8a51f082d5b3b6d07693797637b4028\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"4cb0aea2e250eee35ccfac5f5395cd8f3238a9e5\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"5.10.36\",\n \"lessThan\": \"5.10.271\",\n \"status\": \"affected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.11.20\",\n \"lessThan\": \"5.12\",\n \"status\": \"affected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.12.3\",\n \"lessThan\": \"5.13\",\n \"status\": \"affected\",\n \"versionType\": \"semver\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/btrfs/relocation.c\"\n ],\n \"versions\": [\n {\n \"version\": \"5.13\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"5.13\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.271\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.222\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.189\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.158\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.111\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.53\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/5a247097c5f94b51ffc991b444d998ad6e85875f","https://git.kernel.org/stable/c/6372dd394ea907cd85a7a8063db320ec73dfaed0","https://git.kernel.org/stable/c/9f599d120b2b79d2d937c3935b7cdf2697514283","https://git.kernel.org/stable/c/a01837ae174a2a968c245a30e6dd010f50eaf05d","https://git.kernel.org/stable/c/97a540d72ebcb21853d11f2a56782fe377f358e7","https://git.kernel.org/stable/c/fda1b6636ff1846f00643e791099db5564b547d9","https://git.kernel.org/stable/c/83201804efa4a5168be754e1dfc9b2faee760cac"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-93800","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-93800","identifiers":["CVE-2026-93800"]},"retained":false,"historicalAffected":[]}],"coverage":[]}