{"cve":"CVE-2022-49834","nvd":{"published":"2025-05-01T15:16:06.873","modified":"2026-08-04T10:17:57.087","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/39a3ed68270b079c6b874d4e4727a512b9b4882c","https://git.kernel.org/stable/c/4feedde5486c07ea79787839153a71ca71329c7d","https://git.kernel.org/stable/c/8cccf05fe857a18ee26e20d11a8455a73ffd4efd","https://git.kernel.org/stable/c/9b162e81045266a2d5b44df9dffdf05c54de9cca","https://git.kernel.org/stable/c/afbd1188382a75f6cfe22c0b68533f7f9664f182"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:01:22.920403922+00:00"},"epss":{"cve":"CVE-2022-49834","score":0.00223,"percentile":0.12986,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}