[nginx] QUIC: trial packet decryption in response to invalid key update.

[Sergey Kandaurov]

details:   https://hg.nginx.org/nginx/rev/1bf1b423f268
branches:  
changeset: 9209:1bf1b423f268
user:      Sergey Kandaurov <pluknet at nginx.com>
date:      Wed Feb 14 15:55:34 2024 +0400
description:
QUIC: trial packet decryption in response to invalid key update.

Inspired by RFC 9001, Section 6.3, trial packet decryption with the current
keys is now used to avoid a timing side-channel signal.  Further, this fixes
segfault while accessing missing next keys (ticket #2585).

diffstat:

 src/event/quic/ngx_event_quic_protection.c |  15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diffs (25 lines):

diff -r 2ed3f57dca0a -r 1bf1b423f268 src/event/quic/ngx_event_quic_protection.c
--- a/src/event/quic/ngx_event_quic_protection.c	Wed Feb 14 16:56:28 2024 +0400
+++ b/src/event/quic/ngx_event_quic_protection.c	Wed Feb 14 15:55:34 2024 +0400
@@ -1144,8 +1144,19 @@ ngx_quic_decrypt(ngx_quic_header_t *pkt,
         key_phase = (pkt->flags & NGX_QUIC_PKT_KPHASE) != 0;
 
         if (key_phase != pkt->key_phase) {
-            secret = &pkt->keys->next_key.client;
-            pkt->key_update = 1;
+            if (pkt->keys->next_key.client.ctx != NULL) {
+                secret = &pkt->keys->next_key.client;
+                pkt->key_update = 1;
+
+            } else {
+                /*
+                 * RFC 9001,  6.3. Timing of Receive Key Generation.
+                 *
+                 * Trial decryption to avoid timing side-channel.
+                 */
+                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, pkt->log, 0,
+                               "quic next key missing");
+            }
         }
     }