From: Sergey Kandaurov <pluknet@nginx.com>
Date: Fri, 7 Aug 2020 09:34:11 +0000 (+0300)
Subject: QUIC: fixed possible use-after-free on stream cleanup.
X-Git-Url: http://git.kaiwu.me/postgresql/log/contrib/postgres_fdw/static/gitweb.js?a=commitdiff_plain;h=7d1a1fb6de71ba0ad7ac324a6c43a10a0f5d8ae6;p=nginx.git

QUIC: fixed possible use-after-free on stream cleanup.

A QUIC stream could be destroyed by handler while in ngx_quic_stream_input().
To detect this, ngx_quic_find_stream() is used to check that it still exists.

Previously, a stream id was passed to this routine off the frame structure.
In case of stream cleanup, it is freed along with other frames belonging to
the stream on cleanup.  Then, a cleanup handler reuses last frames to update
MAX_STREAMS and serve other purpose.  Thus, ngx_quic_find_stream() is passed
a reused frame with zeroed out part pointed by stream_id.  If a stream with
id 0x0 still exists, this leads to use-after-free.
---

diff --git a/src/event/ngx_event_quic.c b/src/event/ngx_event_quic.c
index 7c7620322..47c52067e 100644
--- a/src/event/ngx_event_quic.c
+++ b/src/event/ngx_event_quic.c
@@ -3006,6 +3006,7 @@ ngx_quic_handle_stream_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
 static ngx_int_t
 ngx_quic_stream_input(ngx_connection_t *c, ngx_quic_frame_t *frame, void *data)
 {
+    uint64_t                  id;
     ngx_buf_t                *b;
     ngx_event_t              *rev;
     ngx_quic_stream_t        *sn;
@@ -3016,6 +3017,7 @@ ngx_quic_stream_input(ngx_connection_t *c, ngx_quic_frame_t *frame, void *data)
     sn = data;
 
     f = &frame->u.stream;
+    id = f->stream_id;
 
     ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0, "quic existing stream");
 
@@ -3046,7 +3048,7 @@ ngx_quic_stream_input(ngx_connection_t *c, ngx_quic_frame_t *frame, void *data)
     }
 
     /* check if stream was destroyed by handler */
-    if (ngx_quic_find_stream(&qc->streams.tree, f->stream_id) == NULL) {
+    if (ngx_quic_find_stream(&qc->streams.tree, id) == NULL) {
         return NGX_DONE;
     }