[PATCH net-next v3 03/11] tls/sw: Use zero-length sendmsg() without MSG_MORE to flush

[David Howells <dhowells@redhat.com>]

Allow userspace to end a TLS record without supplying any data by calling
send()/sendto()/sendmsg() with no data and no MSG_MORE flag.  This can be
used to flush a previous send/splice that had MSG_MORE or SPLICE_F_MORE set
or a sendfile() that was incomplete.

Without this, a zero-length send to tls-sw is just ignored.  I think
tls-device will do the right thing without modification.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
 net/tls/tls_sw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index cac1adc968e8..6aa6d17888f5 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -945,7 +945,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	struct tls_rec *rec;
 	int required_size;
 	int num_async = 0;
-	bool full_record;
+	bool full_record = false;
 	int record_room;
 	int num_zc = 0;
 	int orig_size;
@@ -971,6 +971,9 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 		}
 	}
 
+	if (!msg_data_left(msg) && eor)
+		goto just_flush;
+
 	while (msg_data_left(msg)) {
 		if (sk->sk_err) {
 			ret = -sk->sk_err;
@@ -1082,6 +1085,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 		 */
 		tls_ctx->pending_open_record_frags = true;
 		copied += try_to_copy;
+just_flush:
 		if (full_record || eor) {
 			ret = bpf_exec_tx_verdict(msg_pl, sk, full_record,
 						  record_type, &copied,