[PATCH net 2/5] tls: Consume empty data records in tls_sw_splice_read()

[Jakub Kicinski <kuba@kernel.org>]

From: Chuck Lever <cel@kernel.org>

A zero-length application_data record decrypts to full_len == 0,
so tls_sw_splice_read() splices zero bytes and returns zero. A zero
return from a splice read means EOF, and the caller tears down a
connection that is still live.

Consume the record and fetch the next one, as tls_sw_read_sock()
does. The cap on consecutive empty records bounds the loop.

When an empty record precedes a close_notify, splice(2) now returns
-EINVAL from the control-record test instead of a false EOF. A
splice that reaches an alert record already reports -EINVAL.

Fixes: c46234ebb4d1 ("tls: RX path for ktls")
Reported-by: Sabrina Dubroca <sd@queasysnail.net>
Closes: https://lore.kernel.org/netdev/akaoXcfamBp8_mYe@krikkit/
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Jakub:
 - rewrite as a loop to avoid the non-error-handling goto
---
 net/tls/tls_sw.c | 48 ++++++++++++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index adf3b26b8a75..b05b9e76bd25 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2044,32 +2044,40 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 	if (err)
 		goto splice_read_end;
 
-	if (!skb_queue_empty(&ctx->rx_list)) {
-		skb = __skb_dequeue(&ctx->rx_list);
-	} else {
-		struct tls_decrypt_arg darg;
+	for (;;) {
+		if (!skb_queue_empty(&ctx->rx_list)) {
+			skb = __skb_dequeue(&ctx->rx_list);
+		} else {
+			struct tls_decrypt_arg darg;
 
-		err = tls_rx_rec_wait(sk, nonblock, true, false);
-		if (err <= 0)
-			goto splice_read_end;
+			err = tls_rx_rec_wait(sk, nonblock, true, false);
+			if (err <= 0)
+				goto splice_read_end;
 
-		memset(&darg.inargs, 0, sizeof(darg.inargs));
+			memset(&darg.inargs, 0, sizeof(darg.inargs));
 
-		err = tls_rx_one_record(sk, NULL, &darg);
-		if (err < 0)
-			goto splice_read_end;
+			err = tls_rx_one_record(sk, NULL, &darg);
+			if (err < 0)
+				goto splice_read_end;
 
-		tls_rx_rec_done(ctx);
-		skb = darg.skb;
-	}
+			tls_rx_rec_done(ctx);
+			skb = darg.skb;
+		}
 
-	rxm = strp_msg(skb);
-	tlm = tls_msg(skb);
+		rxm = strp_msg(skb);
+		tlm = tls_msg(skb);
 
-	/* splice does not support reading control messages */
-	if (tlm->control != TLS_RECORD_TYPE_DATA) {
-		err = -EINVAL;
-		goto splice_requeue;
+		/* splice does not support reading control messages */
+		if (tlm->control != TLS_RECORD_TYPE_DATA) {
+			err = -EINVAL;
+			goto splice_requeue;
+		}
+
+		/* Splicing zero bytes would read as EOF */
+		if (rxm->full_len)
+			break;
+
+		consume_skb(skb);
 	}
 
 	chunk = min_t(unsigned int, rxm->full_len, len);
-- 
2.56.0