[PATCH net-next v2 1/8] tls: bound consecutive no-data records in tls_sw_read_sock()

[Chuck Lever <cel@kernel.org>]

A zero-length application_data record delivers no payload, so
tls_sw_read_sock() never runs the read_actor for one and nothing
decrements desc->count. A peer that streams such records keeps the
loop running, with the socket lock held, for as long as they arrive.
The caller cannot bound the run because read_sock() has not
returned.

Stop after TLS_RX_NODATA_LIMIT consecutive records that deliver no
bytes. Any record that delivers bytes resets the count. Stopping
with nothing copied returns zero, which a read_sock consumer takes
as no progress rather than EOF. Records left queued raise no
further sk_data_ready(), so call the socket's callback before
returning.

Fixes: 3be28e2c9cd0 ("net/tls: Consume empty data records in tls_sw_read_sock()")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 net/tls/tls_sw.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index d1ad31986cf2..c78471c53f2f 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2070,6 +2070,8 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
 	goto splice_read_end;
 }
 
+#define TLS_RX_NODATA_LIMIT	16
+
 int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 		     sk_read_actor_t read_actor)
 {
@@ -2078,6 +2080,7 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 	struct tls_prot_info *prot = &tls_ctx->prot_info;
 	struct strp_msg *rxm = NULL;
 	struct sk_buff *skb = NULL;
+	unsigned int nodata = 0;
 	struct sk_psock *psock;
 	size_t flushed_at = 0;
 	bool released = true;
@@ -2136,14 +2139,22 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 			goto read_sock_requeue;
 		}
 
-		/* An empty data record (legal in TLS 1.3) gives a zero
-		 * read_actor return, indistinguishable from the consumer
-		 * stalling; the used <= 0 path would requeue it at the
-		 * head of rx_list and block all later records. Consume it
-		 * here instead.
+		/* An empty data record gives a zero read_actor return,
+		 * indistinguishable from the consumer stalling; the
+		 * used <= 0 path would requeue it at the head of rx_list
+		 * and block all later records. Consume it here instead.
 		 */
 		if (rxm->full_len == 0) {
+			err = 0;
 			consume_skb(skb);
+			if (++nodata >= TLS_RX_NODATA_LIMIT) {
+				/* tls_rx_reader_release() calls
+				 * saved_data_ready(), not the callback a
+				 * consumer installs after the handshake.
+				 */
+				sk->sk_data_ready(sk);
+				break;
+			}
 			continue;
 		}
 
@@ -2154,6 +2165,7 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 			goto read_sock_requeue;
 		}
 		copied += used;
+		nodata = 0;
 		if (used < rxm->full_len) {
 			rxm->offset += used;
 			rxm->full_len -= used;

-- 
2.55.0