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

SUNRPC: wait for in-flight client TLS handshake callback

xs_tls_handshake_sync() gives xs_tls_handshake_done() a reference to the
lower transport before submitting the handshake request. On timeout or
signal, the synchronous waiter drops that reference after calling
tls_handshake_cancel().

handshake_req_cancel() returns false when handshake_complete() has
already marked the request complete. In that case the completion callback
can still be running, so dropping the callback-owned reference in the
waiter can free the lower transport before xs_tls_handshake_done() stores
xprt_err or drops its own reference.

If cancellation loses to completion, wait until xs_tls_handshake_done()
signals handshake_done and let the callback release its reference. This
mirrors the server-side handshake lifetime handling and keeps the timeout
or signal return value unchanged.