{"id":"CVE-2026-89681","state":"PUBLISHED","title":"nfsd: fix layout fence worker double-reference race","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix layout fence worker double-reference race\n\nThe workqueue core clears WORK_STRUCT_PENDING before the callback\nis invoked, so delayed_work_pending() in lm_breaker_timedout() can\nreturn false while the fence worker is already running. This lets\nthe breaker take a duplicate sc_count reference and schedule a new\nworker that coalesces with the in-progress one. The extra reference\nis never put, leaking the layout stateid.\n\nReplace the racy delayed_work_pending() check with an\nls_fence_inflight boolean set atomically with\nrefcount_inc_not_zero() under ls_lock, and cleared under ls_lock\nbefore the final nfs4_put_stid() on the dispose path; the retry\npath intentionally retains it.  Remove the self-rearm\nmod_delayed_work() at the top of the worker.","publishedAt":"2026-09-11T19:46:04.121Z","updatedAt":"2026-10-19T08:50:54.644Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f52792f484ba2316853736856dde19b7e7458861","status":"affected","lessThan":"a278d361e0e8f242211891193d56483a7a9f47a8","versionType":"git"},{"version":"f52792f484ba2316853736856dde19b7e7458861","status":"affected","lessThan":"8580571227451384399b3fa53fcde19848c48e5a","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4layouts.c","fs/nfsd/state.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4layouts.c","fs/nfsd/state.h"]}],"references":["https://git.kernel.org/stable/c/a278d361e0e8f242211891193d56483a7a9f47a8","https://git.kernel.org/stable/c/8580571227451384399b3fa53fcde19848c48e5a"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89681.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89681","state":"PUBLISHED","datePublished":"2026-09-11T19:46:04.121Z","dateUpdated":"2026-10-19T08:50:54.644Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.748Z"},"containers":{"cna":{"title":"nfsd: fix layout fence worker double-reference race","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix layout fence worker double-reference race\n\nThe workqueue core clears WORK_STRUCT_PENDING before the callback\nis invoked, so delayed_work_pending() in lm_breaker_timedout() can\nreturn false while the fence worker is already running. This lets\nthe breaker take a duplicate sc_count reference and schedule a new\nworker that coalesces with the in-progress one. The extra reference\nis never put, leaking the layout stateid.\n\nReplace the racy delayed_work_pending() check with an\nls_fence_inflight boolean set atomically with\nrefcount_inc_not_zero() under ls_lock, and cleared under ls_lock\nbefore the final nfs4_put_stid() on the dispose path; the retry\npath intentionally retains it.  Remove the self-rearm\nmod_delayed_work() at the top of the worker."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f52792f484ba2316853736856dde19b7e7458861","status":"affected","lessThan":"a278d361e0e8f242211891193d56483a7a9f47a8","versionType":"git"},{"version":"f52792f484ba2316853736856dde19b7e7458861","status":"affected","lessThan":"8580571227451384399b3fa53fcde19848c48e5a","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4layouts.c","fs/nfsd/state.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4layouts.c","fs/nfsd/state.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/a278d361e0e8f242211891193d56483a7a9f47a8"},{"url":"https://git.kernel.org/stable/c/8580571227451384399b3fa53fcde19848c48e5a"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The flaw is in nfsd pNFS SCSI layout fencing (nfsd4_layout_lm_breaker_timedout → nfsd4_layout_fence_worker in fs/nfsd/nfs4layouts.c), reached over NFSv4.1 COMPOUND on TCP/2049: LAYOUTGET installs an FL_LAYOUT lease, then a conflicting OPEN/WRITE hits nfsd_open_break_lease → time_out_leases after recall timeout.\nAC:L - The attacker controls both sides of the delayed_work_pending race: one client holds a SCSI layout and ignores CB_LAYOUTRECALL so the fence worker runs, while other attacker connections spam OPEN/WRITE so concurrent nfsd threads call lm_breaker_timedout while WORK_STRUCT_PENDING is already clear; the sequence is retryable.\nPR:N - Typical nfsd exports accept AUTH_SYS/AUTH_NULL with no cryptographic RPC authentication; EXCHANGE_ID, CREATE_SESSION, OPEN, and LAYOUTGET succeed for any host permitted by the export, so a remote NFSv4.1 client needs no kernel-verified credentials or local account on the server.\nUI:N - The attacker is the NFS client and sends LAYOUTGET plus conflicting OPEN/WRITE compounds against an already-running pNFS SCSI export; no victim user must mount a filesystem, open a file, or take any other action on the host.\nS:U - Impact is kernel nfsd layout-stateid and nfs4_client lifetime on the NFS server host and does not cross a VM, hypervisor, sandbox, or IOMMU security boundary.\nC:H - The unmatched sc_count leaves the nfs4_layout_stateid on nfs4_file.fi_lo_states without pinning nfs4_client; after that client is expired, a later LAYOUTGET walks the list and nfsd4_run_cb dereferences freed cb_clp, a use-after-free that can be reused for arbitrary kernel reads.\nI:H - The same use-after-free of nfs4_client (cl_cb_session, cl_callback_wq, and nfsd4_callback_ops) from nfsd4_recall_file_layout → nfsd4_run_cb enables heap spraying and function-pointer hijack of the CB_LAYOUTRECALL work path.\nA:H - Each won race permanently leaks a layout stateid (and can pin nfs4_client via cl_lo_states); repeating LAYOUTGET/fence races exhausts nfsd state and kernel memory, and the later nfs4_client use-after-free oopses or panics the nfsd thread."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:50:54.644Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}