{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2022-49834", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-05-01T14:05:17.228Z", "datePublished": "2025-05-01T14:09:52.076Z", "dateUpdated": "2026-08-05T08:56:25.358Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:56:25.358Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnilfs2: fix use-after-free bug of ns_writer on remount\n\nIf a nilfs2 filesystem is downgraded to read-only due to metadata\ncorruption on disk and is remounted read/write, or if emergency read-only\nremount is performed, detaching a log writer and synchronizing the\nfilesystem can be done at the same time.\n\nIn these cases, use-after-free of the log writer (hereinafter\nnilfs->ns_writer) can happen as shown in the scenario below:\n\n Task1 Task2\n -------------------------------- ------------------------------\n nilfs_construct_segment\n nilfs_segctor_sync\n init_wait\n init_waitqueue_entry\n add_wait_queue\n schedule\n nilfs_remount (R/W remount case)\n\t\t\t\t nilfs_attach_log_writer\n nilfs_detach_log_writer\n nilfs_segctor_destroy\n kfree\n finish_wait\n _raw_spin_lock_irqsave\n __raw_spin_lock_irqsave\n do_raw_spin_lock\n debug_spin_lock_before <-- use-after-free\n\nWhile Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1\nwaked up, Task1 accesses nilfs->ns_writer which is already freed. This\nscenario diagram is based on the Shigeru Yoshida's post [1].\n\nThis patch fixes the issue by not detaching nilfs->ns_writer on remount so\nthat this UAF race doesn't happen. Along with this change, this patch\nalso inserts a few necessary read-only checks with superblock instance\nwhere only the ns_writer pointer was used to check if the filesystem is\nread-only." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The UAF is reached only through local VFS remount and concurrent sync/fsync on a mounted nilfs2 volume (nilfs_remount → nilfs_detach_log_writer / nilfs_attach_log_writer racing nilfs_construct_segment → nilfs_segctor_sync); nilfs2 is FS_REQUIRES_DEV with no network-facing parser.\nAC:L - The attacker controls both sides of the race—issuing fsync/NILFS_IOCTL_SYNC/writeback that sleeps in nilfs_segctor_sync while concurrently remounting ro/rw to free ns_writer—so success does not depend on conditions outside attacker influence; syzbot reproduced it.\nPR:L - Although remount checks CAP_SYS_ADMIN in sb->s_user_ns and nilfs2 lacks FS_USERNS_MOUNT, an unprivileged desktop/kiosk user can mount a crafted or removable nilfs2 image via udisks2/polkit and have that privileged helper perform remount while driving ordinary fsync/sync, matching CVE-2022-49850.\nUI:N - In the automount/udisks scenario the attacker supplies the volume, obtains the mount, and drives both the syncing thread and the remount themselves; no separate victim action is required.\nS:U - This is a standard in-kernel heap use-after-free within the host kernel's authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - kfree of nilfs_sc_info while another task still holds a pointer into it (finish_wait on sc_wait_request) is a classic heap UAF; reclaim/spray of that object enables arbitrary kernel read primitives.\nI:H - The same UAF of the segment-constructor object lets an attacker control freed wait-queue and related state consumed after wakeup, enabling write/control-flow hijacking consistent with treating exploitable kernel UAFs as High integrity.\nA:H - Even without full exploitation, use of the freed ns_writer in finish_wait/spinlock paths causes kernel oops/panic, fully impacting availability per UAF guidance." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/nilfs2/segment.c", "fs/nilfs2/super.c" ], "versions": [ { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "b2fbf10040216ef5ee270773755fc2f5da65b749", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "39a3ed68270b079c6b874d4e4727a512b9b4882c", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "b4736ab5542112fe0a40f140a0a0b072954f34da", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "9b162e81045266a2d5b44df9dffdf05c54de9cca", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "4feedde5486c07ea79787839153a71ca71329c7d", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "afbd1188382a75f6cfe22c0b68533f7f9664f182", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "b152300d5a1ba4258dacf9916bff20e6a8c7603b", "status": "affected", "versionType": "git" }, { "version": "fe5f171bb272946ce5fbf843ce2f8467d0d41b9a", "lessThan": "8cccf05fe857a18ee26e20d11a8455a73ffd4efd", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/nilfs2/segment.c", "fs/nilfs2/super.c" ], "versions": [ { "version": "2.6.34", "status": "affected" }, { "version": "0", "lessThan": "2.6.34", "status": "unaffected", "versionType": "semver" }, { "version": "4.9.334", "lessThanOrEqual": "4.9.*", "status": "unaffected", "versionType": "semver" }, { "version": "4.14.300", "lessThanOrEqual": "4.14.*", "status": "unaffected", "versionType": "semver" }, { "version": "4.19.267", "lessThanOrEqual": "4.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.4.225", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.155", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.79", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.0.9", "lessThanOrEqual": "6.0.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1", "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": "2.6.34", "versionEndExcluding": "4.9.334" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "4.14.300" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "4.19.267" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.4.225" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.10.155" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.15.79" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.0.9" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.1" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/b2fbf10040216ef5ee270773755fc2f5da65b749" }, { "url": "https://git.kernel.org/stable/c/39a3ed68270b079c6b874d4e4727a512b9b4882c" }, { "url": "https://git.kernel.org/stable/c/b4736ab5542112fe0a40f140a0a0b072954f34da" }, { "url": "https://git.kernel.org/stable/c/9b162e81045266a2d5b44df9dffdf05c54de9cca" }, { "url": "https://git.kernel.org/stable/c/4feedde5486c07ea79787839153a71ca71329c7d" }, { "url": "https://git.kernel.org/stable/c/afbd1188382a75f6cfe22c0b68533f7f9664f182" }, { "url": "https://git.kernel.org/stable/c/b152300d5a1ba4258dacf9916bff20e6a8c7603b" }, { "url": "https://git.kernel.org/stable/c/8cccf05fe857a18ee26e20d11a8455a73ffd4efd" } ], "title": "nilfs2: fix use-after-free bug of ns_writer on remount", "x_generator": { "engine": "bippy-1.2.0" } } } }