High [CVE-2026-72422] fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE conn->preauth_info is shared connection state (struct preauth_integrity_info, kmalloc-96) that is allocated and freed by the SMB2 NEGOTIATE handler and read by the response send path. smb2_handle_negotiate() allocates conn->preauth_info, and on a deassemble_neg_contexts() failure kfrees it and sets it to NULL.

Both the allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the connection srv_mutex), which is held across the whole handler body.

The response send path smb3_preauth_hash_rsp(), called from the send: block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences conn->preauth_info->Preauth_HashValue (via ksmbd_gen_preauth_integrity_hash()) without taking conn_lock.

When a client drives two SMB2 NEGOTIATE requests on the same connection, one worker can free conn->preauth_info on the failing-negotiate path while a concurrent send-path worker is reading it, producing a slab use-after-free read (KASAN-confirmed).

The send-path read tested conn->preauth_info for NULL but raced with the free that occurs between the NULL check and the dereference, so the NULL guard alone does not close the window.

Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat package: kernel.