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changeset 9208:2ed3f57dca0a

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QUIC: fixed unsent MTU probe acknowledgement. Previously if an MTU probe send failed early in ngx_quic_frame_sendto() due to allocation error or congestion control, the application level packet number was not increased, but was still saved as MTU probe packet number. Later when a packet with this number was acknowledged, the unsent MTU probe was acknowledged as well. This could result in discovering a bigger MTU than supported by the path, which could lead to EMSGSIZE (Message too long) errors while sending further packets. The problem existed since PMTUD was introduced in 58afcd72446f (1.25.2). Back then only the unlikely memory allocation error could trigger it. However in efcdaa66df2e congestion control was added to ngx_quic_frame_sendto() which can now trigger the issue with a higher probability.
author Roman Arutyunyan <arut@nginx.com>
date Wed, 14 Feb 2024 16:56:28 +0400
parents 73eb75bee30f
children 1bf1b423f268
files src/event/quic/ngx_event_quic_migration.c
diffstat 1 files changed, 12 insertions(+), 7 deletions(-) [+]
line wrap: on
line diff
--- a/src/event/quic/ngx_event_quic_migration.c
+++ b/src/event/quic/ngx_event_quic_migration.c
@@ -909,6 +909,7 @@ static ngx_int_t
 ngx_quic_send_path_mtu_probe(ngx_connection_t *c, ngx_quic_path_t *path)
 {
     size_t                  mtu;
+    uint64_t                pnum;
     ngx_int_t               rc;
     ngx_uint_t              log_error;
     ngx_quic_frame_t       *frame;
@@ -925,7 +926,7 @@ ngx_quic_send_path_mtu_probe(ngx_connect
 
     qc = ngx_quic_get_connection(c);
     ctx = ngx_quic_get_send_ctx(qc, ssl_encryption_application);
-    path->mtu_pnum[path->tries] = ctx->pnum;
+    pnum = ctx->pnum;
 
     ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
                    "quic path seq:%uL send probe "
@@ -943,14 +944,18 @@ ngx_quic_send_path_mtu_probe(ngx_connect
     path->mtu = mtu;
     c->log_error = log_error;
 
+    if (rc == NGX_OK) {
+        path->mtu_pnum[path->tries] = pnum;
+        return NGX_OK;
+    }
+
+    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic path seq:%uL rejected mtu:%uz",
+                   path->seqnum, path->mtud);
+
     if (rc == NGX_ERROR) {
         if (c->write->error) {
             c->write->error = 0;
-
-            ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                           "quic path seq:%uL rejected mtu:%uz",
-                           path->seqnum, path->mtud);
-
             return NGX_DECLINED;
         }
 
@@ -976,7 +981,7 @@ ngx_quic_handle_path_mtu(ngx_connection_
         pnum = path->mtu_pnum[i];
 
         if (pnum == NGX_QUIC_UNSET_PN) {
-            break;
+            continue;
         }
 
         if (pnum < min || pnum > max) {