CVE-2026-93255 - Vulnerability Details

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Linux Subscribe	Linux Kernel Subscribe

Link	Providers
https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec
https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31

Type	Values Removed	Values Added
Description		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: 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 [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() \| [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.
Title		btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-93255", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-17T16:02:15.096Z", "datePublished": "2026-09-24T15:51:42.056Z", "dateUpdated": "2026-09-24T15:51:42.056Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-09-24T15:51:42.056Z"}, "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."}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/btrfs/disk-io.c", "fs/btrfs/extent_io.c"], "versions": [{"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"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/btrfs/disk-io.c", "fs/btrfs/extent_io.c"], "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-rc1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.2", "versionEndExcluding": "7.2.6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.2", "versionEndExcluding": "7.3-rc1"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.1.8"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec"}, {"url": "https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31"}], "title": "btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock", "x_generator": {"engine": "bippy-1.2.0"}}}}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["fs/btrfs/disk-io.c", "fs/btrfs/extent_io.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "2073f3d97b0c5d34fe64812d1237e37bd79c17ec", "status": "affected", "version": "83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb", "versionType": "git"}, {"lessThan": "690c2accacb1aca91ab8186d15dee56da8723f31", "status": "affected", "version": "83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb", "versionType": "git"}, {"status": "affected", "version": "b0c33c0628c5b0678fcae2e05e7b2764149248f8", "versionType": "git"}, {"lessThan": "7.2", "status": "affected", "version": "7.1.8", "versionType": "semver"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["fs/btrfs/disk-io.c", "fs/btrfs/extent_io.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "7.2"}, {"lessThan": "7.2", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "7.2.*", "status": "unaffected", "version": "7.2.6", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "7.3-rc1", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "cveTags": [], "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."}], "id": "CVE-2026-93255", "lastModified": "2026-09-24T16:17:22.007", "metrics": {}, "published": "2026-09-24T16:17:22.007", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/2073f3d97b0c5d34fe64812d1237e37bd79c17ec"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/690c2accacb1aca91ab8186d15dee56da8723f31"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Received"}

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