tls: Flush backlog before waiting for a new record

While lock_sock is held, incoming TCP segments land on
sk->sk_backlog rather than sk->sk_receive_queue.
tls_rx_rec_wait() inspects only sk_receive_queue, so backlog
data remains invisible. For non-blocking callers (read_sock,
and recvmsg or splice_read with MSG_DONTWAIT) this causes a
spurious -EAGAIN. For blocking callers it forces an
unnecessary sleep/wakeup cycle.

Flush the backlog inside tls_rx_rec_wait() before checking
sk_receive_queue so the strparser can parse newly-arrived
segments immediately. On the next loop iteration
tls_read_flush_backlog() may redundantly flush, but this
path is cold and the cost is negligible.

Backlog processing can run tcp_reset(), which calls
tcp_done_with_error() to set sk->sk_err = ECONNRESET and then
tcp_done() to set sk->sk_shutdown = SHUTDOWN_MASK. The pre-existing
top-of-loop sk_err check already ran before the flush, so the
freshly-set error would be masked by the next-line sk_shutdown test
returning 0 (EOF). Re-check sk_err immediately before the sk_shutdown
test so a connection abort surfaces as -ECONNRESET rather than a clean
EOF.

Commit f508262ae9 ("tls: Preserve sk_err across recvmsg() when
data has been copied") gave the top-of-loop sk_err check a
has_copied split. The recheck applies the same handling: when the
caller has already copied bytes, sk_err is reported but preserved
so the error surfaces on the next call; otherwise sock_error()
consumes it so the error is reported exactly once.

Suggested-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/netdev/ahgHgQ84RCc8uYrG@krikkit/
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260604-tls-read-sock-v12-6-b114efa6e3e2@oracle.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/tls/tls_sw.c

@@ -1400,6 +1400,8 @@ tls_rx_rec_wait(struct sock *sk, struct sk_psock *psock, bool nonblock,
 		if (ret < 0)
 			return ret;
 
+		if (sk_flush_backlog(sk))
+			released = true;
 		if (!skb_queue_empty(&sk->sk_receive_queue)) {
 			/* Defer notification to the exit point; this thread
 			 * will consume the record directly.
@@ -1409,6 +1411,16 @@ tls_rx_rec_wait(struct sock *sk, struct sk_psock *psock, bool nonblock,
 				break;
 		}
 
+		/* sk_flush_backlog() can run tcp_reset(), which sets
+		 * sk_err and then sk_shutdown via tcp_done(). Recheck
+		 * sk_err here so a connection abort surfaces as the
+		 * actual error rather than a clean EOF.
+		 */
+		if (sk->sk_err) {
+			if (has_copied)
+				return -READ_ONCE(sk->sk_err);
+			return sock_error(sk);
+		}
 		if (sk->sk_shutdown & RCV_SHUTDOWN)
 			return 0;