net/tls: fix no wakeup on partial reads

When tls_sw_recvmsg() partially copies a record it pops that
record from ctx->recv_pkt and places it on rx_list.

Next iteration of tls_sw_recvmsg() reads from rx_list via
process_rx_list() before it enters the decryption loop.
If there is no more records to be read tls_wait_data()
will put the process on the wait queue and got to sleep.
This is incorrect, because some data was already copied
in process_rx_list().

In case of RPC connections process may never get woken up,
because peer also simply blocks in read().

I think this may also fix a similar issue when BPF is at
play, because after __tcp_bpf_recvmsg() returns some data
we subtract it from len and use continue to restart the
loop, but len could have just reached 0, so again we'd
sleep unnecessarily. That's added by:
commit d3b18ad3 ("tls: add bpf support to sk_msg handling")

Fixes: 692d7b5d ("tls: Fix recvmsg() to be able to peek across multiple records")
Reported-by: David Beckett <david.beckett@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Tested-by: David Beckett <david.beckett@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_sw.c

@@ -1719,7 +1719,7 @@ int tls_sw_recvmsg(struct sock *sk,
 	len = len - copied;
 	timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
 
-	do {
+	while (len && (decrypted + copied < target || ctx->recv_pkt)) {
 		bool retain_skb = false;
 		bool zc = false;
 		int to_decrypt;
@@ -1850,11 +1850,7 @@ int tls_sw_recvmsg(struct sock *sk,
 		} else {
 			break;
 		}
-
-		/* If we have a new message from strparser, continue now. */
-		if (decrypted + copied >= target && !ctx->recv_pkt)
-			break;
-	} while (len);
+	}
 
 recv_end:
 	if (num_async) {