{"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"}}}}