CVE-2026-89788 — ksmbd: fix tree connection use-after-free in smb2_tree_connect()

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix tree connection use-after-free in smb2_tree_connect()

ksmbd_tree_conn_connect() publishes a new tree connection in sess->tree_conns with a single reference and returns its pointer to smb2_tree_connect(). The handler continues to initialize the object and build the response after publication. A concurrent session logoff can erase the connection and drop that reference, freeing the object while the handler still uses it.

BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90 smb2_tree_connect (fs/smb/server/smb2pdu.c:2872) handle_ksmbd_work process_one_work worker_thread kthread

After xa_store() succeeds, take a second reference before releasing tree_conns_lock. The original reference belongs to the xarray entry and the second belongs to the creating smb2_tree_connect() handler.

Keep the references balanced in every path:

- On normal exit or an error after publication, smb2_tree_connect() drops its creator reference. Error cleanup also calls ksmbd_tree_conn_disconnect(), which drops the xarray reference only if it removes the exact entry. - SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop its xarray reference. The request's existing lookup reference remains owned by the request and is released by the existing cleanup. - Session LOGOFF removes each entry and drops its xarray reference. If it wins the race, later cleanup sees that the entry i…

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CVE-2026-89788 — ksmbd: fix tree connection use-after-free in smb2_tree_connect()