[PATCH 3/3] rxrpc: recheck RXRPC_CALL_TX_NO_MORE after sleeping in rxrpc_send_data()

Commit ae4f89989479 ("rxrpc: Fix ability to add more data to a call
once MSG_MORE deasserted") added the RXRPC_CALL_TX_NO_MORE flag and an
entry check in rxrpc_send_data() to stop late sends on a finalized
call. However, the check runs only once at function entry: when the
transmit window is full, wait_for_space drops call->user_mutex and
sleeps, during which another thread sharing the same user_call_ID can
finalize the call (queue the LAST packet, setting TX_NO_MORE and
clearing send_queue). Upon waking, the reload path only re-verifies
the shutdown flag and call state - and a just-finalized call is still
in RXRPC_CALL_CLIENT_SEND_REQUEST until its data is hard-acked - so
the thread proceeds to rxrpc_alloc_txqueue() with send_queue == NULL
but tx_queue != NULL, triggering:

	WARNING: net/rxrpc/sendmsg.c:297 at rxrpc_alloc_txqueue

and returning a spurious -ENOMEM. The call state itself is entirely
legal at that point; the WARN_ON's implied assumption that
send_queue == NULL implies tx_queue == NULL simply does not hold after
finalization.

Re-check RXRPC_CALL_TX_NO_MORE in the reload path after reacquiring
user_mutex, mirroring the entry check, and bail out with -EPROTO.

Found by the autokbug dynamic kernel fuzzer at Tencent Yunding Lab.

Fixes: ae4f89989479 ("rxrpc: Fix ability to add more data to a call once MSG_MORE deasserted")
Signed-off-by: Henry Martin <redacted>
---
 net/rxrpc/sendmsg.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index ed2c9a51005ad..b39af552c6b46 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c

@@ -358,6 +358,14 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 	if (txb)
 		rxrpc_see_txbuf(txb, rxrpc_txbuf_see_send_more);
 
+	ret = -EPROTO;
+	if (test_bit(RXRPC_CALL_TX_NO_MORE, &call->flags)) {
+		trace_rxrpc_abort(call->debug_id, rxrpc_sendmsg_late_send,
+				  call->cid, call->call_id, call->rx_consumed,
+				  0, -EPROTO);
+		goto maybe_error;
+	}
+
 	ret = -EPIPE;
 	if (sk->sk_shutdown & SEND_SHUTDOWN)
 		goto maybe_error;

-- 
2.43.0