{"id":"CVE-2026-93255","revision":null,"records":[{"revision":"1a0c4076f08c4fdc8e580835605ea208","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-93255","aliases":[],"title":"btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock","description":"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.","state":0,"publishedAt":"2026-09-24T15:51:42.056+00:00","modifiedAt":"2026-10-19T09:08:08.727+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/disk-io.c\",\n \"fs/btrfs/extent_io.c\"\n ],\n \"versions\": [\n {\n \"version\": \"f5427cab065641a4553d38bb8c4932b8d456c7a7\",\n \"lessThan\": \"8f7285d608ed0db7c9f09f341547db5ce1351090\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb\",\n \"lessThan\": \"2073f3d97b0c5d34fe64812d1237e37bd79c17ec\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb\",\n \"lessThan\": \"690c2accacb1aca91ab8186d15dee56da8723f31\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"b0c33c0628c5b0678fcae2e05e7b2764149248f8\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"7.1.8\",\n \"lessThan\": \"7.2\",\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/disk-io.c\",\n \"fs/btrfs/extent_io.c\"\n ],\n \"versions\": [\n {\n \"version\": \"7.2\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"7.2\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2.6\",\n \"lessThanOrEqual\": \"7.2.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.3\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/8f7285d608ed0db7c9f09f341547db5ce1351090","https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec","https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-93255","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-93255","identifiers":["CVE-2026-93255"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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