[nginx] QUIC: fixed post-close use-after-free.

[Roman Arutyunyan]

details:   https://hg.nginx.org/nginx/rev/d59277dd3d8c
branches:  
changeset: 9112:d59277dd3d8c
user:      Roman Arutyunyan <arut at nginx.com>
date:      Mon May 22 15:59:42 2023 +0400
description:
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).

diffstat:

 src/event/quic/ngx_event_quic.c         |   4 ++--
 src/event/quic/ngx_event_quic_ack.c     |   1 +
 src/event/quic/ngx_event_quic_streams.c |  18 +++++++++++++-----
 3 files changed, 16 insertions(+), 7 deletions(-)

diffs (73 lines):

diff -r 68fa4b86ed46 -r d59277dd3d8c src/event/quic/ngx_event_quic.c
--- a/src/event/quic/ngx_event_quic.c	Sun May 21 04:38:45 2023 +0300
+++ b/src/event/quic/ngx_event_quic.c	Mon May 22 15:59:42 2023 +0400
@@ -844,7 +844,7 @@ ngx_quic_handle_packet(ngx_connection_t 
                               "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 
 
     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 -r 68fa4b86ed46 -r d59277dd3d8c src/event/quic/ngx_event_quic_ack.c
--- a/src/event/quic/ngx_event_quic_ack.c	Sun May 21 04:38:45 2023 +0300
+++ b/src/event/quic/ngx_event_quic_ack.c	Mon May 22 15:59:42 2023 +0400
@@ -806,6 +806,7 @@ void ngx_quic_lost_handler(ngx_event_t *
 
     if (ngx_quic_detect_lost(c, NULL) != NGX_OK) {
         ngx_quic_close_connection(c, NGX_ERROR);
+        return;
     }
 
     ngx_quic_connstate_dbg(c);
diff -r 68fa4b86ed46 -r d59277dd3d8c src/event/quic/ngx_event_quic_streams.c
--- a/src/event/quic/ngx_event_quic_streams.c	Sun May 21 04:38:45 2023 +0300
+++ b/src/event/quic/ngx_event_quic_streams.c	Mon May 22 15:59:42 2023 +0400
@@ -1084,7 +1084,8 @@ ngx_quic_stream_cleanup_handler(void *da
 {
     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 *da
                    "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);
 }