CVE-2026-93255
In the Linux kernel, the following vulnerability has been resolved:
btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock
[FALSE ALERTS] There is a bug report that the warning inside invalidate_and_check_btree_folios() got triggered during btrfs/298:
[CAUSE] In that invalidate_and_check_btree_folios() we wait for the eb to finish its read, then check if it's only held by us and the btree inode.
If not, then do a warning as it may be still held, and could cause problems.
But there is a small window where the check can lead to false alerts:
Thread A (Read endio) | Thread B (Unmount) ----------------------------------+------------------------------------- end_bbio_meta_read() | | The eb has one extra ref held | | by the reader, and has | | EXTENT_BUFFER_READING flag set | invalidate_and_check_btree_folios() | | | |- clear_extent_buffer_reading() | | | | |- wait_on_bit_io(); | | | The EXTENT_BUFFER_READING flag is | | | cleared | | |- if (refcount_read(eb->refs) > 2) | | The eb is held by the read, us | | and btree inode, thus it | | will trigger the warning |- free_extent_buffer() |
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[FIX] Introduce a helper, free_extent_buffer_clear_reading().
If the new parameter, @clear_reading, is set, we will hold the spinlock at the beginning of free_extent_buffer_clear_reading() to make sure the EXTENT_BUFFER_READING flag is cleared inside the same critical section of decreasing refs.
Now free_extent_buffer() will just call free_extent_buffer_clear_reading() with @clear_reading set to false, so no behavior change.
But for end_bbio_meta_read(), it will not clear_extent_buffer_reading() directly, but pass @clear_reading as true.
Then inside invalidate_and_check_btree_folios(), hold the refs_lock before reading refs. So that we eliminate the race window completely.
Detalles técnicos trazas, registros y código del informe original
BTRFS info (device sdd): first mount of filesystem f9bf732a-a19b-44b9-99a7-614ddff168e2 BTRFS info (device sdd): using crc32c checksum algorithm BTRFS error (device sdd): failed to find fsid cb2fdb42-b638-4f2f-badd-4127467ba674 when attempting to open seed devices BTRFS error (device sdd): failed to read chunk tree: -2 ------------[ cut here ]------------ WARNING: disk-io.c:3342 at invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs], CPU#4: mount/125993 CPU: 4 UID: 0 PID: 125993 Comm: mount Tainted: G W OE 7.1.0-rc7-custom+ #1 PREEMPT(full) Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250812-19.fc42 08/12/2025 Call trace: invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs] (P) open_ctree+0x1f50/0x23b0 [btrfs] btrfs_get_tree+0x89c/0xc48 [btrfs] vfs_get_tree+0x30/0x110 vfs_cmd_create+0x58/0xe8 __arm64_sys_fsconfig+0x39c/0x518 invoke_syscall.constprop.0+0x48/0x120 el0_svc_common.constprop.0+0x40/0xe8 do_el0_svc+0x24/0x38 el0_svc+0x50/0x310 el0t_64_sync_handler+0xa0/0xe8 el0t_64_sync+0x198/0x1a0 ---[ end trace 0000000000000000 ]--- BTRFS warning (device sdd): unable to release extent buffer 365985792 owner 3 gen 17 refs 3 flags 0x5
CVSS
NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.19%
- Percentil entre todas las CVEs puntuadas: 8
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
JSON original (NVD)
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{
"id": "CVE-2026-93255",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb",
"lessThan": "2073f3d97b0c5d34fe64812d1237e37bd79c17ec",
"versionType": "git"
},
{
"status": "affected",
"version": "83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb",
"lessThan": "690c2accacb1aca91ab8186d15dee56da8723f31",
"versionType": "git"
},
{
"status": "affected",
"version": "b0c33c0628c5b0678fcae2e05e7b2764149248f8",
"versionType": "git"
},
{
"status": "affected",
"version": "7.1.8",
"lessThan": "7.2",
"versionType": "semver"
}
],
"programFiles": [
"fs/btrfs/disk-io.c",
"fs/btrfs/extent_io.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "7.2"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "7.2",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "7.2.6",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3-rc1",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/btrfs/disk-io.c",
"fs/btrfs/extent_io.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-09-24T16:17:22.007",
"references": [
{
"url": "https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "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."
}
],
"lastModified": "2026-09-24T16:17:22.007",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}