changeset 6351:497d0cff8ace

Resolver: fixed use-after-free memory accesses with CNAME. When several requests were waiting for a response, then after getting a CNAME response only the last request's context had the name updated. Contexts of other requests had the wrong name. This name was used by ngx_resolve_name_done() to find the node to remove the request context from. When the name was wrong, the request could not be properly cancelled, its context was freed but stayed linked to the node's waiting list. This happened e.g. when the first request was aborted or timed out before the resolving completed. When it completed, this triggered a use-after-free memory access by calling ctx->handler of already freed request context. The bug manifests itself by "could not cancel <name> resolving" alerts in error_log. When a request was responded with a CNAME, the request context kept the pointer to the original node's rn->u.cname. If the original node expired before the resolving timed out or completed with an error, this would trigger a use-after-free memory access via ctx->name in ctx->handler(). The fix is to keep ctx->name unmodified. The name from context is no longer used by ngx_resolve_name_done(). Instead, we now keep the pointer to resolver node to which this request is linked. Keeping the original name intact also improves logging.
author Roman Arutyunyan <arut@nginx.com>
date Tue, 26 Jan 2016 16:46:59 +0300
parents a5767988c022
children ff9b32c0e141
files src/core/ngx_resolver.c src/core/ngx_resolver.h
diffstat 2 files changed, 39 insertions(+), 43 deletions(-) [+]
line wrap: on
line diff
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -59,7 +59,7 @@ ngx_int_t ngx_udp_connect(ngx_udp_connec
 static void ngx_resolver_cleanup(void *data);
 static void ngx_resolver_cleanup_tree(ngx_resolver_t *r, ngx_rbtree_t *tree);
 static ngx_int_t ngx_resolve_name_locked(ngx_resolver_t *r,
-    ngx_resolver_ctx_t *ctx);
+    ngx_resolver_ctx_t *ctx, ngx_str_t *name);
 static void ngx_resolver_expire(ngx_resolver_t *r, ngx_rbtree_t *tree,
     ngx_queue_t *queue);
 static ngx_int_t ngx_resolver_send_query(ngx_resolver_t *r,
@@ -376,7 +376,7 @@ ngx_resolve_name(ngx_resolver_ctx_t *ctx
 
     /* lock name mutex */
 
-    rc = ngx_resolve_name_locked(r, ctx);
+    rc = ngx_resolve_name_locked(r, ctx, &ctx->name);
 
     if (rc == NGX_OK) {
         return NGX_OK;
@@ -403,7 +403,6 @@ ngx_resolve_name(ngx_resolver_ctx_t *ctx
 void
 ngx_resolve_name_done(ngx_resolver_ctx_t *ctx)
 {
-    uint32_t              hash;
     ngx_resolver_t       *r;
     ngx_resolver_ctx_t   *w, **p;
     ngx_resolver_node_t  *rn;
@@ -425,9 +424,7 @@ ngx_resolve_name_done(ngx_resolver_ctx_t
 
     if (ctx->state == NGX_AGAIN || ctx->state == NGX_RESOLVE_TIMEDOUT) {
 
-        hash = ngx_crc32_short(ctx->name.data, ctx->name.len);
-
-        rn = ngx_resolver_lookup_name(r, &ctx->name, hash);
+        rn = ctx->node;
 
         if (rn) {
             p = &rn->waiting;
@@ -472,20 +469,22 @@ done:
 
 
 static ngx_int_t
-ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
+ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx,
+    ngx_str_t *name)
 {
     uint32_t              hash;
     ngx_int_t             rc;
+    ngx_str_t             cname;
     ngx_uint_t            naddrs;
     ngx_addr_t           *addrs;
     ngx_resolver_ctx_t   *next, *last;
     ngx_resolver_node_t  *rn;
 
-    ngx_strlow(ctx->name.data, ctx->name.data, ctx->name.len);
-
-    hash = ngx_crc32_short(ctx->name.data, ctx->name.len);
-
-    rn = ngx_resolver_lookup_name(r, &ctx->name, hash);
+    ngx_strlow(name->data, name->data, name->len);
+
+    hash = ngx_crc32_short(name->data, name->len);
+
+    rn = ngx_resolver_lookup_name(r, name, hash);
 
     if (rn) {
 
@@ -559,10 +558,10 @@ ngx_resolve_name_locked(ngx_resolver_t *
 
             if (ctx->recursion++ < NGX_RESOLVER_MAX_RECURSION) {
 
-                ctx->name.len = rn->cnlen;
-                ctx->name.data = rn->u.cname;
-
-                return ngx_resolve_name_locked(r, ctx);
+                cname.len = rn->cnlen;
+                cname.data = rn->u.cname;
+
+                return ngx_resolve_name_locked(r, ctx, &cname);
             }
 
             last->next = rn->waiting;
@@ -602,6 +601,11 @@ ngx_resolve_name_locked(ngx_resolver_t *
             rn->waiting = ctx;
             ctx->state = NGX_AGAIN;
 
+            do {
+                ctx->node = rn;
+                ctx = ctx->next;
+            } while (ctx);
+
             return NGX_AGAIN;
         }
 
@@ -640,14 +644,14 @@ ngx_resolve_name_locked(ngx_resolver_t *
             return NGX_ERROR;
         }
 
-        rn->name = ngx_resolver_dup(r, ctx->name.data, ctx->name.len);
+        rn->name = ngx_resolver_dup(r, name->data, name->len);
         if (rn->name == NULL) {
             ngx_resolver_free(r, rn);
             return NGX_ERROR;
         }
 
         rn->node.key = hash;
-        rn->nlen = (u_short) ctx->name.len;
+        rn->nlen = (u_short) name->len;
         rn->query = NULL;
 #if (NGX_HAVE_INET6)
         rn->query6 = NULL;
@@ -656,7 +660,7 @@ ngx_resolve_name_locked(ngx_resolver_t *
         ngx_rbtree_insert(&r->name_rbtree, &rn->node);
     }
 
-    rc = ngx_resolver_create_name_query(r, rn, &ctx->name);
+    rc = ngx_resolver_create_name_query(r, rn, name);
 
     if (rc == NGX_ERROR) {
         goto failed;
@@ -720,6 +724,11 @@ ngx_resolve_name_locked(ngx_resolver_t *
 
     ctx->state = NGX_AGAIN;
 
+    do {
+        ctx->node = rn;
+        ctx = ctx->next;
+    } while (ctx);
+
     return NGX_AGAIN;
 
 failed:
@@ -842,6 +851,7 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx
             ctx->next = rn->waiting;
             rn->waiting = ctx;
             ctx->state = NGX_AGAIN;
+            ctx->node = rn;
 
             /* unlock addr mutex */
 
@@ -927,6 +937,7 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx
     /* unlock addr mutex */
 
     ctx->state = NGX_AGAIN;
+    ctx->node = rn;
 
     return NGX_OK;
 
@@ -957,17 +968,11 @@ failed:
 void
 ngx_resolve_addr_done(ngx_resolver_ctx_t *ctx)
 {
-    in_addr_t             addr;
     ngx_queue_t          *expire_queue;
     ngx_rbtree_t         *tree;
     ngx_resolver_t       *r;
     ngx_resolver_ctx_t   *w, **p;
-    struct sockaddr_in   *sin;
     ngx_resolver_node_t  *rn;
-#if (NGX_HAVE_INET6)
-    uint32_t              hash;
-    struct sockaddr_in6  *sin6;
-#endif
 
     r = ctx->resolver;
 
@@ -996,21 +1001,7 @@ ngx_resolve_addr_done(ngx_resolver_ctx_t
 
     if (ctx->state == NGX_AGAIN || ctx->state == NGX_RESOLVE_TIMEDOUT) {
 
-        switch (ctx->addr.sockaddr->sa_family) {
-
-#if (NGX_HAVE_INET6)
-        case AF_INET6:
-            sin6 = (struct sockaddr_in6 *) ctx->addr.sockaddr;
-            hash = ngx_crc32_short(sin6->sin6_addr.s6_addr, 16);
-            rn = ngx_resolver_lookup_addr6(r, &sin6->sin6_addr, hash);
-            break;
-#endif
-
-        default: /* AF_INET */
-            sin = (struct sockaddr_in *) ctx->addr.sockaddr;
-            addr = ntohl(sin->sin_addr.s_addr);
-            rn = ngx_resolver_lookup_addr(r, addr);
-        }
+        rn = ctx->node;
 
         if (rn) {
             p = &rn->waiting;
@@ -2014,9 +2005,12 @@ ngx_resolver_process_a(ngx_resolver_t *r
         rn->waiting = NULL;
 
         if (ctx) {
-            ctx->name = name;
-
-            (void) ngx_resolve_name_locked(r, ctx);
+
+            for (next = ctx; next; next = next->next) {
+                next->node = NULL;
+            }
+
+            (void) ngx_resolve_name_locked(r, ctx, &name);
         }
 
         ngx_resolver_free(r, rn->query);
--- a/src/core/ngx_resolver.h
+++ b/src/core/ngx_resolver.h
@@ -161,6 +161,8 @@ struct ngx_resolver_ctx_s {
     ngx_uint_t                quick;  /* unsigned  quick:1; */
     ngx_uint_t                recursion;
     ngx_event_t              *event;
+
+    ngx_resolver_node_t      *node;
 };