{"cve":"CVE-2026-64142","nvd":{"published":"2026-07-19T16:17:56.103","modified":"2026-08-17T19:40:06.100","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: close durable scavenger races against m_fp_list lookups\n\nksmbd_durable_scavenger() has two related races against any walker\nthat iterates f_ci->m_fp_list, including ksmbd_lookup_fd_inode()\n(used by ksmbd_vfs_rename) and the share-mode checks in\nfs/smb/server/smb_common.c.\n\n(1) fp->node list-head reuse.  Durable-preserved handles can remain\nlinked on f_ci->m_fp_list after session teardown so share-mode checks\nstill see them while the handle is reconnectable.  The scavenger\ncollected expired handles by adding fp->node to a local\nscavenger_list after removing them from the global durable idr.\nBecause fp->node is the same list_head used by m_fp_list,\nlist_add(&fp->node, &scavenger_list) overwrites the m_fp_list links\nand corrupts both lists.  CONFIG_DEBUG_LIST can report this on the\nshare-mode walk path.\n\n(2) Refcount race against m_fp_list walkers.  The scavenger qualifies\nan expired durable handle with atomic_read(&fp->refcount) > 1 and\nfp->conn under global_ft.lock, removes fp from global_ft, then drops\nglobal_ft.lock before unlinking fp from m_fp_list and freeing it.\nDuring that gap fp is still linked on m_fp_list with f_state ==\nFP_INITED.  ksmbd_lookup_fd_inode() under m_lock read calls\nksmbd_fp_get() (atomic_inc_not_zero on refcount that is still 1) and\ntakes a live reference; the scavenger then unlinks and frees fp\nwhile the holder owns a reference, leading to UAF on the holder's\nsubsequent ksmbd_fd_put() and on any field reads performed by a\nconcurrent share-mode walker that iterates m_fp_list without taking\nksmbd_fp_get() (smb_check_perm_dleases-like paths).\n\nFix both:\n\n  * Stop reusing fp->node as a scavenger-private list node.  Remove\n    one expired handle from global_ft under global_ft.lock, take an\n    explicit transient reference, drop the lock, unlink fp->node\n    from m_fp_list under f_ci->m_lock, then drop both the durable\n    lifetime and transient references with atomic_sub_and_test(2,\n    &fp->refcount).  If the scavenger is the last putter the close\n    runs there; otherwise an in-flight holder that already raced\n    through the m_fp_list lookup owns the final close via its\n    ksmbd_fd_put() path.  The one-at-a-time disposal can rescan the\n    durable idr when multiple handles expire in the same pass, but\n    durable scavenging is a background expiration path and the final\n    full scan recomputes min_timeout before the next wait.\n\n  * Clear fp->persistent_id inside __ksmbd_remove_durable_fd() right\n    after idr_remove(), so a delayed final close from a holder that\n    snatched fp does not re-issue idr_remove() on a persistent id\n    that idr_alloc_cyclic() in ksmbd_open_durable_fd() may have\n    already handed out to a brand-new durable handle.\n\n  * Bypass the per-conn open_files_count decrement in\n    __put_fd_final() when fp is detached from any session table\n    (fp->conn cleared by session_fd_check() at durable preserve --\n    paired with the volatile_id clear at unpublish, so checking\n    fp->conn alone is sufficient).  The walker that owns the final\n    close runs from an unrelated work->conn whose\n    stats.open_files_count never tracked this durable fp; without\n    this guard the holder would underflow that unrelated counter.\n\nThe two races are folded into one patch because patch (1) alone\ncleans up the corrupted list but leaves a deterministic UAF window\nfor m_fp_list walkers that the transient-reference and\npersistent_id discipline in (2) close; bisecting onto an\nintermediate state would land on a UAF that pre-patch chaos merely\nmade less reproducible.\n\nValidation:\n  * CONFIG_DEBUG_LIST coverage for the list_head reuse path.\n  * KASAN-enabled direct SMB2 durable-handle coverage that exercised\n    ksmbd_durable_scavenger() and non-NULL ksmbd_lookup_fd_inode()\n    returns while durable handles expired under concurrent rename\n    lookups, with no KASAN, UAF, list-corruption, ODEBUG, or WARNING\n    reports.\n---truncated---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/1f8f3246d55f89350a1a67bdf3744b7241048e4e","https://git.kernel.org/stable/c/3a436932eb397e909d0607d76a8325abd9d85a35","https://git.kernel.org/stable/c/5da69a65b282d2276de22e5194ba0f88c836170c","https://git.kernel.org/stable/c/95f072ef934ca00711d510676b8792cbf59a5aae","https://git.kernel.org/stable/c/bf736184d063da1a552ffeff0481813599a182cc"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:45:36.895656543+00:00"},"epss":{"cve":"CVE-2026-64142","score":0.00705,"percentile":0.53357,"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."]}