[PATCH net-next v2 3/8] tls: consume empty data records in tls_sw_splice_read()

[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_recvmsg()
does. Test for a pending signal before each retry, so a peer that
streams empty records cannot make the splicing task unkillable.

When an empty record precedes a close_notify, splice(2) now returns
-EINVAL from the control-record test instead of the false EOF it
returned before. 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>
---
 net/tls/tls_sw.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index ee50b9028264..79a807e51bc7 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2018,6 +2018,7 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 	struct sock *sk = sock->sk;
 	struct tls_msg *tlm;
 	struct sk_buff *skb;
+	bool released = true;
 	ssize_t copied = 0;
 	int chunk;
 	int err;
@@ -2031,13 +2032,14 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 	if (err)
 		goto splice_read_end;
 
+retry:
 	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, flags & SPLICE_F_NONBLOCK,
-				      true, false);
+				      released, false);
 		if (err <= 0)
 			goto splice_read_end;
 
@@ -2049,6 +2051,9 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 
 		tls_rx_rec_done(ctx);
 		skb = darg.skb;
+
+		/* The retry's wait runs with the socket lock still held. */
+		released = false;
 	}
 
 	rxm = strp_msg(skb);
@@ -2060,6 +2065,19 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 		goto splice_requeue;
 	}
 
+	/* Splicing zero bytes reads as EOF to the caller. */
+	if (rxm->full_len == 0) {
+		consume_skb(skb);
+		if (signal_pending(current)) {
+			long timeo;
+
+			timeo = sock_rcvtimeo(sk, flags & SPLICE_F_NONBLOCK);
+			err = sock_intr_errno(timeo);
+			goto splice_read_end;
+		}
+		goto retry;
+	}
+
 	chunk = min_t(unsigned int, rxm->full_len, len);
 	copied = skb_splice_bits(skb, sk, rxm->offset, pipe, chunk, flags);
 	if (copied < 0)

-- 
2.55.0