{"api_version":"1","generated_at":"2026-09-12T12:32:03+00:00","cve":"CVE-2026-89708","urls":{"html":"https://cve.report/CVE-2026-89708","api":"https://cve.report/api/cve/CVE-2026-89708.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-89708","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-89708"},"summary":{"title":"nfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown\n\nAfter a DESTROY_SESSION the per-session teardown path can free a\nsession while rpciod still holds an inflight callback rpc_task that\ndereferences clp->cl_cb_session.  nfsd4_probe_callback_sync() flushes\ncl_callback_wq, but once nfsd4_run_cb_work() has called\nrpc_call_async() the rpc_task lives on rpciod; flushing the workqueue\ndoes not wait for it.  rpc_shutdown_client() does drain rpciod tasks,\nbut uses a 1-second wait_event_timeout — tasks stuck in rpc_delay()\n(e.g. 2-second NFS4ERR_DELAY retries) can outlive the drain.\n\n    destroy path                       rpciod\n    ------------                       ------\n    unhash_session(ses)\n    nfsd4_probe_callback_sync(clp)\n      flush_workqueue(cl_callback_wq)\n      /* returns; rpc_task still live */\n    nfsd4_put_session_locked(ses)\n    free_session(ses) -> kfree(ses)\n                                       nfsd4_cb_sequence_done()\n                                         reads cb_clp->cl_cb_session\n                                         /* freed slab */\n\nA second window exists in nfsd4_process_cb_update().  When\n__nfsd4_find_backchannel() returns NULL because unhash_session() has\nalready removed the destroyed session from cl_sessions,\nsetup_callback_client() takes the v4.1 early return so\nclp->cl_cb_session = ses never fires and the field retains a pointer\nto the about-to-be-freed session.\n\nFix both by converting cl_cb_session to an RCU-protected pointer:\n\n  - Move the cl_cb_session = ses assignment in setup_callback_client()\n    to after rpc_create() succeeds, so it is only published when a\n    working backchannel exists.  Clear cl_cb_session on the error\n    return in nfsd4_process_cb_update().  Both stores use\n    rcu_assign_pointer().\n\n  - Annotate cl_cb_session with __rcu.  All rpciod-side readers use\n    rcu_read_lock()/rcu_dereference() and check for NULL, bailing to\n    the appropriate error or requeue path:\n    encode_cb_sequence4args(), decode_cb_sequence4resok(),\n    nfsd41_cb_get_slot(), nfsd41_cb_release_slot(),\n    nfsd4_cb_prepare(), and nfsd4_cb_sequence_done().\n\n  - Switch __free_session() from kfree() to kfree_rcu() so the\n    session slab is not reclaimed until after an RCU grace period,\n    guaranteeing that rpciod readers inside rcu_read_lock() never\n    dereference freed memory.\n\n  - Pass the session pointer to the nfsd_cb_seq_status and\n    nfsd_cb_free_slot tracepoints instead of having them re-read\n    cl_cb_session.\n\n  - nfsd4_cb_prepare() calls rpc_exit() when the session is NULL,\n    routing through the done/release path to requeue the callback.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-11 20:19:58","updated_at":"2026-09-11 20:19:58"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25","name":"https://git.kernel.org/stable/c/13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/01c5d5f58a5db9b0ee5afba2e49d3157788687b2","name":"https://git.kernel.org/stable/c/01c5d5f58a5db9b0ee5afba2e49d3157788687b2","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f164eb52b6f3cbf40f07fe379f9f421f88e02f76","name":"https://git.kernel.org/stable/c/f164eb52b6f3cbf40f07fe379f9f421f88e02f76","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89708","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89708","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected dcbeaa68dbbdacbbb330a86c7fc95a28473fc209 f164eb52b6f3cbf40f07fe379f9f421f88e02f76 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected dcbeaa68dbbdacbbb330a86c7fc95a28473fc209 13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected dcbeaa68dbbdacbbb330a86c7fc95a28473fc209 01c5d5f58a5db9b0ee5afba2e49d3157788687b2 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 2.6.38","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 2.6.38 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.50 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.4 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3-rc1 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["fs/nfsd/nfs4callback.c","fs/nfsd/nfs4state.c","fs/nfsd/state.h","fs/nfsd/trace.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"f164eb52b6f3cbf40f07fe379f9f421f88e02f76","status":"affected","version":"dcbeaa68dbbdacbbb330a86c7fc95a28473fc209","versionType":"git"},{"lessThan":"13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25","status":"affected","version":"dcbeaa68dbbdacbbb330a86c7fc95a28473fc209","versionType":"git"},{"lessThan":"01c5d5f58a5db9b0ee5afba2e49d3157788687b2","status":"affected","version":"dcbeaa68dbbdacbbb330a86c7fc95a28473fc209","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["fs/nfsd/nfs4callback.c","fs/nfsd/nfs4state.c","fs/nfsd/state.h","fs/nfsd/trace.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"2.6.38"},{"lessThan":"2.6.38","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.50","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.4","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3-rc1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.50","versionStartIncluding":"2.6.38","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.4","versionStartIncluding":"2.6.38","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3-rc1","versionStartIncluding":"2.6.38","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown\n\nAfter a DESTROY_SESSION the per-session teardown path can free a\nsession while rpciod still holds an inflight callback rpc_task that\ndereferences clp->cl_cb_session.  nfsd4_probe_callback_sync() flushes\ncl_callback_wq, but once nfsd4_run_cb_work() has called\nrpc_call_async() the rpc_task lives on rpciod; flushing the workqueue\ndoes not wait for it.  rpc_shutdown_client() does drain rpciod tasks,\nbut uses a 1-second wait_event_timeout — tasks stuck in rpc_delay()\n(e.g. 2-second NFS4ERR_DELAY retries) can outlive the drain.\n\n    destroy path                       rpciod\n    ------------                       ------\n    unhash_session(ses)\n    nfsd4_probe_callback_sync(clp)\n      flush_workqueue(cl_callback_wq)\n      /* returns; rpc_task still live */\n    nfsd4_put_session_locked(ses)\n    free_session(ses) -> kfree(ses)\n                                       nfsd4_cb_sequence_done()\n                                         reads cb_clp->cl_cb_session\n                                         /* freed slab */\n\nA second window exists in nfsd4_process_cb_update().  When\n__nfsd4_find_backchannel() returns NULL because unhash_session() has\nalready removed the destroyed session from cl_sessions,\nsetup_callback_client() takes the v4.1 early return so\nclp->cl_cb_session = ses never fires and the field retains a pointer\nto the about-to-be-freed session.\n\nFix both by converting cl_cb_session to an RCU-protected pointer:\n\n  - Move the cl_cb_session = ses assignment in setup_callback_client()\n    to after rpc_create() succeeds, so it is only published when a\n    working backchannel exists.  Clear cl_cb_session on the error\n    return in nfsd4_process_cb_update().  Both stores use\n    rcu_assign_pointer().\n\n  - Annotate cl_cb_session with __rcu.  All rpciod-side readers use\n    rcu_read_lock()/rcu_dereference() and check for NULL, bailing to\n    the appropriate error or requeue path:\n    encode_cb_sequence4args(), decode_cb_sequence4resok(),\n    nfsd41_cb_get_slot(), nfsd41_cb_release_slot(),\n    nfsd4_cb_prepare(), and nfsd4_cb_sequence_done().\n\n  - Switch __free_session() from kfree() to kfree_rcu() so the\n    session slab is not reclaimed until after an RCU grace period,\n    guaranteeing that rpciod readers inside rcu_read_lock() never\n    dereference freed memory.\n\n  - Pass the session pointer to the nfsd_cb_seq_status and\n    nfsd_cb_free_slot tracepoints instead of having them re-read\n    cl_cb_session.\n\n  - nfsd4_cb_prepare() calls rpc_exit() when the session is NULL,\n    routing through the done/release path to requeue the callback."}],"providerMetadata":{"dateUpdated":"2026-09-11T19:46:24.061Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/f164eb52b6f3cbf40f07fe379f9f421f88e02f76"},{"url":"https://git.kernel.org/stable/c/13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25"},{"url":"https://git.kernel.org/stable/c/01c5d5f58a5db9b0ee5afba2e49d3157788687b2"}],"title":"nfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-89708","datePublished":"2026-09-11T19:46:24.061Z","dateReserved":"2026-09-11T19:38:34.751Z","dateUpdated":"2026-09-11T19:46:24.061Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-11 20:19:58","lastModifiedDate":"2026-09-11 20:19:58","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"89708","Ordinal":"1","Title":"nfsd: RCU-protect cl_cb_session to fix use-after-free on session","CVE":"CVE-2026-89708","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"89708","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown\n\nAfter a DESTROY_SESSION the per-session teardown path can free a\nsession while rpciod still holds an inflight callback rpc_task that\ndereferences clp->cl_cb_session.  nfsd4_probe_callback_sync() flushes\ncl_callback_wq, but once nfsd4_run_cb_work() has called\nrpc_call_async() the rpc_task lives on rpciod; flushing the workqueue\ndoes not wait for it.  rpc_shutdown_client() does drain rpciod tasks,\nbut uses a 1-second wait_event_timeout — tasks stuck in rpc_delay()\n(e.g. 2-second NFS4ERR_DELAY retries) can outlive the drain.\n\n    destroy path                       rpciod\n    ------------                       ------\n    unhash_session(ses)\n    nfsd4_probe_callback_sync(clp)\n      flush_workqueue(cl_callback_wq)\n      /* returns; rpc_task still live */\n    nfsd4_put_session_locked(ses)\n    free_session(ses) -> kfree(ses)\n                                       nfsd4_cb_sequence_done()\n                                         reads cb_clp->cl_cb_session\n                                         /* freed slab */\n\nA second window exists in nfsd4_process_cb_update().  When\n__nfsd4_find_backchannel() returns NULL because unhash_session() has\nalready removed the destroyed session from cl_sessions,\nsetup_callback_client() takes the v4.1 early return so\nclp->cl_cb_session = ses never fires and the field retains a pointer\nto the about-to-be-freed session.\n\nFix both by converting cl_cb_session to an RCU-protected pointer:\n\n  - Move the cl_cb_session = ses assignment in setup_callback_client()\n    to after rpc_create() succeeds, so it is only published when a\n    working backchannel exists.  Clear cl_cb_session on the error\n    return in nfsd4_process_cb_update().  Both stores use\n    rcu_assign_pointer().\n\n  - Annotate cl_cb_session with __rcu.  All rpciod-side readers use\n    rcu_read_lock()/rcu_dereference() and check for NULL, bailing to\n    the appropriate error or requeue path:\n    encode_cb_sequence4args(), decode_cb_sequence4resok(),\n    nfsd41_cb_get_slot(), nfsd41_cb_release_slot(),\n    nfsd4_cb_prepare(), and nfsd4_cb_sequence_done().\n\n  - Switch __free_session() from kfree() to kfree_rcu() so the\n    session slab is not reclaimed until after an RCU grace period,\n    guaranteeing that rpciod readers inside rcu_read_lock() never\n    dereference freed memory.\n\n  - Pass the session pointer to the nfsd_cb_seq_status and\n    nfsd_cb_free_slot tracepoints instead of having them re-read\n    cl_cb_session.\n\n  - nfsd4_cb_prepare() calls rpc_exit() when the session is NULL,\n    routing through the done/release path to requeue the callback.","Type":"Description","Title":"nfsd: RCU-protect cl_cb_session to fix use-after-free on session"}]}}}