tls: don't rely on tx_work during send()

With async crypto, we rely on tx_work to actually transmit records
once encryption completes. But while send() is running, both the
tx_lock and socket lock are held, so tx_work_handler cannot process
the queue of encrypted records, and simply reschedules itself. During
a large send(), this could last a long time, and use a lot of memory.

Transmit any pending encrypted records before restarting the main
loop of tls_sw_sendmsg_locked.

Fixes: a42055e ("net/tls: Add support for async encryption of records for performance")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/8396631478f70454b44afb98352237d33f48d34d.1760432043.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: qsn

net/tls/tls_sw.c

@@ -1152,6 +1152,13 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 				} else if (ret != -EAGAIN)
 					goto send_end;
 			}
+
+			/* Transmit if any encryptions have completed */
+			if (test_and_clear_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask)) {
+				cancel_delayed_work(&ctx->tx_work.work);
+				tls_tx_records(sk, msg->msg_flags);
+			}
+
 			continue;
 rollback_iter:
 			copied -= try_to_copy;
@@ -1207,6 +1214,12 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 					goto send_end;
 				}
 			}
+
+			/* Transmit if any encryptions have completed */
+			if (test_and_clear_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask)) {
+				cancel_delayed_work(&ctx->tx_work.work);
+				tls_tx_records(sk, msg->msg_flags);
+			}
 		}
 
 		continue;