Resolver: fixed crashes in timeout handler.

If one or more requests were waiting for a response, then after
getting a CNAME response, the timeout event on the first request
remained active, pointing to the wrong node with an empty
rn->waiting list, and that could cause either null pointer
dereference or use-after-free memory access if this timeout
expired.

If several requests were waiting for a response, and the first
request terminated (e.g., due to client closing a connection),
other requests were left without a timeout and could potentially
wait indefinitely.

This is fixed by introducing per-request independent timeouts.
This change also reverts 954867a2f0a6 and 5004210e8c78.

1 files changed, 6 insertions, 7 deletions

diff --git a/src/core/ngx_resolver.h b/src/core/ngx_resolver.h
index d3519fb6f..22f249595 100644
--- a/src/core/ngx_resolver.h
+++ b/src/core/ngx_resolver.h
@@ -51,15 +51,11 @@ typedef void (*ngx_resolver_handler_pt)(ngx_resolver_ctx_t *ctx);
 
 
 typedef struct {
-    /* PTR: resolved name, A: name to resolve */
-    u_char                   *name;
-
+    ngx_rbtree_node_t         node;
     ngx_queue_t               queue;
 
-    /* event ident must be after 3 pointers as in ngx_connection_t */
-    ngx_int_t                 ident;
-
-    ngx_rbtree_node_t         node;
+    /* PTR: resolved name, A: name to resolve */
+    u_char                   *name;
 
 #if (NGX_HAVE_INET6)
     /* PTR: IPv6 address to resolve (IPv4 address is in rbtree node key) */
@@ -147,6 +143,9 @@ struct ngx_resolver_ctx_s {
     ngx_resolver_t           *resolver;
     ngx_udp_connection_t     *udp_connection;
 
+    /* event ident must be after 3 pointers as in ngx_connection_t */
+    ngx_int_t                 ident;
+
     ngx_int_t                 state;
     ngx_str_t                 name;