{"schema":"threatline.record/2","record":{"id":"CVE-2026-93255","aliases":[],"summary":"btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock\n\n[FALSE ALERTS]\nThere is a bug report that the warning inside\ninvalidate_and_check_btree_folios() got triggered during btrfs/298:\n\n BTRFS info (device sdd): first mount of filesystem f9bf732a-a19b-44b9-99a7-614ddff168e2\n BTRFS info (device sdd): using crc32c checksum algorithm\n BTRFS error (device sdd): failed to find fsid cb2fdb42-b638-4f2f-badd-4127467ba674 when attempting to open seed devices\n BTRFS error (device sdd): failed to read chunk tree: -2\n ------------[ cut here ]------------\n WARNING: disk-io.c:3342 at invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs], CPU#4: mount/125993\n CPU: 4 UID: 0 PID: 125993 Comm: mount Tainted: G        W  OE       7.1.0-rc7-custom+ #1 PREEMPT(full)\n Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250812-19.fc42 08/12/2025\n Call trace:\n  invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs] (P)\n  open_ctree+0x1f50/0x23b0 [btrfs]\n  btrfs_get_tree+0x89c/0xc48 [btrfs]\n  vfs_get_tree+0x30/0x110\n  vfs_cmd_create+0x58/0xe8\n  __arm64_sys_fsconfig+0x39c/0x518\n  invoke_syscall.constprop.0+0x48/0x120\n  el0_svc_common.constprop.0+0x40/0xe8\n  do_el0_svc+0x24/0x38\n  el0_svc+0x50/0x310\n  el0t_64_sync_handler+0xa0/0xe8\n  el0t_64_sync+0x198/0x1a0\n ---[ end trace 0000000000000000 ]---\n BTRFS warning (device sdd): unable to release extent buffer 365985792 owner 3 gen 17 refs 3 flags 0x5\n\n[CAUSE]\nIn that invalidate_and_check_btree_folios() we wait for the eb to finish\nits read, then check if it's only held by us and the btree inode.\n\nIf not, then do a warning as it may be still held, and could cause\nproblems.\n\nBut there is a small window where the check can lead to false alerts:\n\n    Thread A (Read endio)         |        Thread B (Unmount)\n----------------------------------+-------------------------------------\n end_bbio_meta_read()             |\n | The eb has one extra ref held  |\n | by the reader, and has         |\n | EXTENT_BUFFER_READING flag set | invalidate_and_check_btree_folios()\n |                                | |\n |- clear_extent_buffer_reading() | |\n |                                | |- wait_on_bit_io();\n |                                | |  The EXTENT_BUFFER_READING flag is\n |                                | |  cleared\n |                                | |- if (refcount_read(eb->refs) > 2)\n |                                |    The eb is held by the read, us\n |                                |    and btree inode, thus it\n |                                |    will trigger the warning\n |- free_extent_buffer()          |\n\n[FIX]\nIntroduce a helper, free_extent_buffer_clear_reading().\n\nIf the new parameter, @clear_reading, is set, we will hold the spinlock\nat the beginning of free_extent_buffer_clear_reading() to make sure the\nEXTENT_BUFFER_READING flag is cleared inside the same critical section\nof decreasing refs.\n\nNow free_extent_buffer() will just call\nfree_extent_buffer_clear_reading() with @clear_reading set to false, so\nno behavior change.\n\nBut for end_bbio_meta_read(), it will not clear_extent_buffer_reading()\ndirectly, but pass @clear_reading as true.\n\nThen inside invalidate_and_check_btree_folios(), hold the refs_lock\nbefore reading refs.\nSo that we eliminate the race window completely.","categories":["Operating systems"],"product":"Linux","vendor":"Linux","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"f5427cab065641a4553d38bb8c4932b8d456c7a7","lessThan":"8f7285d608ed0db7c9f09f341547db5ce1351090","status":"affected","versionType":"git"},{"version":"83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb","lessThan":"2073f3d97b0c5d34fe64812d1237e37bd79c17ec","status":"affected","versionType":"git"},{"version":"83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb","lessThan":"690c2accacb1aca91ab8186d15dee56da8723f31","status":"affected","versionType":"git"},{"version":"b0c33c0628c5b0678fcae2e05e7b2764149248f8","status":"affected","versionType":"git"},{"version":"7.1.8","lessThan":"7.2","status":"affected","versionType":"semver"}],"defaultStatus":"unaffected"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Linux","vendor":"Linux","versions":[{"version":"7.2","status":"affected"},{"version":"0","lessThan":"7.2","status":"unaffected","versionType":"semver"},{"version":"7.2.6","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}],"defaultStatus":"affected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"8f7285d608ed0db7c9f09f341547db5ce1351090","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"2073f3d97b0c5d34fe64812d1237e37bd79c17ec","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"690c2accacb1aca91ab8186d15dee56da8723f31","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","source_modified_at":"2026-10-19T09:08:08.727Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"Linux","ecosystem":null},"version":"7.2","basis":"first unaffected version stated in the CVE record"}],"cvss":null,"severity":null,"kev":{"listed":false},"epss":{"probability":0.00198,"percentile":0.09058,"score_date":"2026-10-23"},"published_at":"2026-09-24T15:51:42.056Z","modified_at":"2026-10-19T09:08:08.727Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-93255","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-19T09:08:08.727Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-93255","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://git.kernel.org/stable/c/8f7285d608ed0db7c9f09f341547db5ce1351090"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-19T09:08:08.727Z","content_hash":"fbfd33785475e33070b0d43fe60b75570786ff3c81b7dc9fd923f5ea74be3a3f"}}