QUIC: fixed post-close use-after-free.

Previously, ngx_quic_close_connection() could be called in a way that QUIC
connection was accessed after the call.  In most cases the connection is not
closed right away, but close timeout is scheduled.  However, it's not always
the case.  Also, if the close process started earlier for a different reason,
calling ngx_quic_close_connection() may actually close the connection.  The
connection object should not be accessed after that.

Now, when possible, return statement is added to eliminate post-close connection
object access.  In other places ngx_quic_close_connection() is substituted with
posting close event.

Also, the new way of closing connection in ngx_quic_stream_cleanup_handler()
fixes another problem in this function.  Previously it passed stream connection
instead of QUIC connection to ngx_quic_close_connection().  This could result
in incomplete connection shutdown.  One consequence of that could be that QUIC
streams were freed without shutting down their application contexts.  This could
result in another use-after-free.

Found by Coverity (CID 1530402).

3 files changed, 16 insertions, 7 deletions

diff --git a/src/event/quic/ngx_event_quic.c b/src/event/quic/ngx_event_quic.c
index b4033bc3f..b559c485d 100644
--- a/src/event/quic/ngx_event_quic.c
+++ b/src/event/quic/ngx_event_quic.c
@@ -844,7 +844,7 @@ ngx_quic_handle_packet(ngx_connection_t *c, ngx_quic_conf_t *conf,
                               "quic stateless reset packet detected");
 
                 qc->draining = 1;
-                ngx_quic_close_connection(c, NGX_OK);
+                ngx_post_event(&qc->close, &ngx_posted_events);
 
                 return NGX_OK;
             }
@@ -1390,7 +1390,7 @@ ngx_quic_handle_frames(ngx_connection_t *c, ngx_quic_header_t *pkt)
 
     if (do_close) {
         qc->draining = 1;
-        ngx_quic_close_connection(c, NGX_OK);
+        ngx_post_event(&qc->close, &ngx_posted_events);
     }
 
     if (pkt->path != qc->path && nonprobing) {
diff --git a/src/event/quic/ngx_event_quic_ack.c b/src/event/quic/ngx_event_quic_ack.c
index 062b065f9..21ee888c9 100644
--- a/src/event/quic/ngx_event_quic_ack.c
+++ b/src/event/quic/ngx_event_quic_ack.c
@@ -806,6 +806,7 @@ void ngx_quic_lost_handler(ngx_event_t *ev)
 
     if (ngx_quic_detect_lost(c, NULL) != NGX_OK) {
         ngx_quic_close_connection(c, NGX_ERROR);
+        return;
     }
 
     ngx_quic_connstate_dbg(c);
diff --git a/src/event/quic/ngx_event_quic_streams.c b/src/event/quic/ngx_event_quic_streams.c
index 6664dfd7b..b4b0eda05 100644
--- a/src/event/quic/ngx_event_quic_streams.c
+++ b/src/event/quic/ngx_event_quic_streams.c
@@ -1084,7 +1084,8 @@ ngx_quic_stream_cleanup_handler(void *data)
 {
     ngx_connection_t *c = data;
 
-    ngx_quic_stream_t  *qs;
+    ngx_quic_stream_t      *qs;
+    ngx_quic_connection_t  *qc;
 
     qs = c->quic;
 
@@ -1092,16 +1093,23 @@ ngx_quic_stream_cleanup_handler(void *data)
                    "quic stream id:0x%xL cleanup", qs->id);
 
     if (ngx_quic_shutdown_stream(c, NGX_RDWR_SHUTDOWN) != NGX_OK) {
-        ngx_quic_close_connection(c, NGX_ERROR);
-        return;
+        goto failed;
     }
 
     qs->connection = NULL;
 
     if (ngx_quic_close_stream(qs) != NGX_OK) {
-        ngx_quic_close_connection(c, NGX_ERROR);
-        return;
+        goto failed;
     }
+
+    return;
+
+failed:
+
+    qc = ngx_quic_get_connection(qs->parent);
+    qc->error = NGX_QUIC_ERR_INTERNAL_ERROR;
+
+    ngx_post_event(&qc->close, &ngx_posted_events);
 }