[PATCH v2 3/8] SUNRPC: treat every TLS error alert as fatal

[Chuck Lever <cel@kernel.org>]

svc_tcp_sock_process_cmsg() decides whether an alert ends the session
by reading the alert's level octet. RFC 8446 Section 6 retired that
field. The severity is implicit in the description, and a receiver
treats every alert listed in Section 6.2 as an error alert
"regardless of the AlertLevel in the message". A peer that aborts
with unexpected_message but leaves the legacy octet set to warning
makes the server return -EAGAIN. svc_tcp_recvfrom() then leaves a
dead TLS session attached to an open transport. NFSD keeps polling
it.

Decide from the alert description instead. close_notify and
user_canceled are the closure alerts (RFC 8446 Section 6.1). Every
other description ends the session, including one this kernel does
not recognize.

Fixes: 39067dda1d86 ("SUNRPC: Use new helpers to handle TLS Alerts")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 net/sunrpc/svcsock.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 2e5107a1fb89..756db84e4aec 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -257,8 +257,18 @@ svc_tcp_sock_process_cmsg(struct socket *sock, struct msghdr *msg,
 		break;
 	case TLS_RECORD_TYPE_ALERT:
 		tls_alert_recv(sock->sk, msg, &level, &description);
-		ret = (level == TLS_ALERT_LEVEL_FATAL) ?
-			-ENOTCONN : -EAGAIN;
+		/* RFC 8446 Section 6: every alert but a closure alert is
+		 * an error alert, whatever the legacy AlertLevel octet
+		 * says.
+		 */
+		switch (description) {
+		case TLS_ALERT_DESC_CLOSE_NOTIFY:
+		case TLS_ALERT_DESC_USER_CANCELED:
+			ret = -EAGAIN;
+			break;
+		default:
+			ret = -ENOTCONN;
+		}
 		break;
 	default:
 		/* discard this record type */

-- 
2.54.0