Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  ksmbd: close durable scavenger races against m_fp_list lookups  ksmbd_durable_scavenger() has two related races against any walker that iterates f_ci->m_fp_list, including ksmbd_lookup_fd_inode() (used by ksmbd_vfs_rename) and the share-mode checks in fs/smb/server/smb_common.c.  (1) fp->node list-head reuse.  Durable-preserved handles can remain linked on f_ci->m_fp_list after session teardown so share-mode checks still see them while the handle is reconnectable.  The scavenger collected expired handles by adding fp->node to a local scavenger_list after removing them from the global durable idr. Because fp->node is the same list_head used by m_fp_list, list_add(&fp->node, &scavenger_list) overwrites the m_fp_list links and corrupts both lists.  CONFIG_DEBUG_LIST can report this on the share-mode walk path.  (2) Refcount race against m_fp_list walkers.  The scavenger qualifies an expired durable handle with atomic_read(&fp->refcount) > 1 and fp->conn under global_ft.lock, removes fp from global_ft, then drops global_ft.lock before unlinking fp from m_fp_list and freeing it. During that gap fp is still linked on m_fp_list with f_state == FP_INITED.  ksmbd_lookup_fd_inode() under m_lock read calls ksmbd_fp_get() (atomic_inc_not_zero on refcount that is still 1) and takes a live reference; the scavenger then unlinks and frees fp while the holder owns a reference, leading to UAF on the holder's subsequent ksmbd_fd_put() and on any field reads performed by a concurrent share-mode walker that iterates m_fp_list without taking ksmbd_fp_get() (smb_check_perm_dleases-like paths).  Fix both:    * Stop reusing fp->node as a scavenger-private list node.  Remove     one expired handle from global_ft under global_ft.lock, take an     explicit transient reference, drop the lock, unlink fp->node     from m_fp_list under f_ci->m_lock, then drop both the durable     lifetime and transient references with atomic_sub_and_test(2,     &fp->refcount).  If the scavenger is the last putter the close     runs there; otherwise an in-flight holder that already raced     through the m_fp_list lookup owns the final close via its     ksmbd_fd_put() path.  The one-at-a-time disposal can rescan the     durable idr when multiple handles expire in the same pass, but     durable scavenging is a background expiration path and the final     full scan recomputes min_timeout before the next wait.    * Clear fp->persistent_id inside __ksmbd_remove_durable_fd() right     after idr_remove(), so a delayed final close from a holder that     snatched fp does not re-issue idr_remove() on a persistent id     that idr_alloc_cyclic() in ksmbd_open_durable_fd() may have     already handed out to a brand-new durable handle.    * Bypass the per-conn open_files_count decrement in     __put_fd_final() when fp is detached from any session table     (fp->conn cleared by session_fd_check() at durable preserve --     paired with the volatile_id clear at unpublish, so checking     fp->conn alone is sufficient).  The walker that owns the final     close runs from an unrelated work->conn whose     stats.open_files_count never tracked this durable fp; without     this guard the holder would underflow that unrelated counter.  The two races are folded into one patch because patch (1) alone cleans up the corrupted list but leaves a deterministic UAF window for m_fp_list walkers that the transient-reference and persistent_id discipline in (2) close; bisecting onto an intermediate state would land on a UAF that pre-patch chaos merely made less reproducible.  Validation:   * CONFIG_DEBUG_LIST coverage for the list_head reuse path.   * KASAN-enabled direct SMB2 durable-handle coverage that exercised     ksmbd_durable_scavenger() and non-NULL ksmbd_lookup_fd_inode()     returns while durable handles expired under concurrent rename     lookups, with no KASAN, UAF, list-corruption, ODEBUG, or WARNING     reports. ---truncated---