Subject: [PATCH] net/tls: avoid TCP window full during ->read_sock()

From: Hannes Reinecke <[email-masked]>
Date: Thu, 3 Aug 2023 12:08:09 +0200

When flushing the backlog after decoding each record in ->read_sock()
we may end up with really long records, causing a TCP window full as
the TCP window would only be increased again after we process the
record. So we should rather process the record first to allow the
TCP window to be increased again before flushing the backlog.

Signed-off-by: Hannes Reinecke <[email-masked]>
---
 net/tls/tls_sw.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 9c1f13541708..57db189b29b0 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2240,7 +2240,6 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 			tlm = tls_msg(skb);
 		} else {
 			struct tls_decrypt_arg darg;
-			int to_decrypt;
 
 			err = tls_rx_rec_wait(sk, NULL, true, released);
 			if (err <= 0)
@@ -2248,20 +2247,16 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 
 			memset(&darg.inargs, 0, sizeof(darg.inargs));
 
-			rxm = strp_msg(tls_strp_msg(ctx));
-			tlm = tls_msg(tls_strp_msg(ctx));
-
-			to_decrypt = rxm->full_len - prot->overhead_size;
-
 			err = tls_rx_one_record(sk, NULL, &darg);
 			if (err < 0) {
 				tls_err_abort(sk, -EBADMSG);
 				goto read_sock_end;
 			}
 
-			released = tls_read_flush_backlog(sk, prot, rxm->full_len, to_decrypt,
-							  decrypted, &flushed_at);
 			skb = darg.skb;
+			/* TLS 1.3 may have updated the length by more than overhead */
+			rxm = strp_msg(skb);
+			tlm = tls_msg(skb);
 			decrypted += rxm->full_len;
 
 			tls_rx_rec_done(ctx);
@@ -2280,6 +2275,12 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 			goto read_sock_requeue;
 		}
 		copied += used;
+		/*
+		 * flush backlog after processing the TLS record, otherwise we might
+		 * end up with really large records and triggering a TCP window full.
+		 */
+		released = tls_read_flush_backlog(sk, prot, decrypted - copied, decrypted,
+						  copied, &flushed_at);
 		if (used < rxm->full_len) {
 			rxm->offset += used;
 			rxm->full_len -= used;
-- 
2.35.3