File: 0007-Resolver-fixed-use-after-free-memory-accesses-with-C.patch

package info (click to toggle)
nginx 1.6.2-5+deb8u1~bpo70+1
  • links: PTS, VCS
  • area: main
  • in suites: wheezy-backports
  • size: 13,340 kB
  • sloc: ansic: 144,236; perl: 7,373; sh: 1,325; ruby: 789; makefile: 137; asm: 48; awk: 36; cpp: 18
file content (248 lines) | stat: -rw-r--r-- 8,323 bytes parent folder | download | duplicates (3)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
From: Roman Arutyunyan <arut@nginx.com>
Date: Tue, 26 Jan 2016 16:46:59 +0300
Subject: 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.
---
 src/core/ngx_resolver.c | 72 +++++++++++++++++++++++--------------------------
 src/core/ngx_resolver.h |  2 ++
 2 files changed, 35 insertions(+), 39 deletions(-)

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
index 1899564..2bd754c 100644
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -54,7 +54,7 @@ ngx_int_t ngx_udp_connect(ngx_udp_connection_t *uc);
 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,
@@ -370,7 +370,7 @@ 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;
@@ -397,7 +397,6 @@ 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;
@@ -419,9 +418,7 @@ ngx_resolve_name_done(ngx_resolver_ctx_t *ctx)
 
     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;
@@ -462,20 +459,22 @@ 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);
+    ngx_strlow(name->data, name->data, name->len);
 
-    hash = ngx_crc32_short(ctx->name.data, ctx->name.len);
+    hash = ngx_crc32_short(name->data, name->len);
 
-    rn = ngx_resolver_lookup_name(r, &ctx->name, hash);
+    rn = ngx_resolver_lookup_name(r, name, hash);
 
     if (rn) {
 
@@ -549,10 +548,10 @@ ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
 
             if (ctx->recursion++ < NGX_RESOLVER_MAX_RECURSION) {
 
-                ctx->name.len = rn->cnlen;
-                ctx->name.data = rn->u.cname;
+                cname.len = rn->cnlen;
+                cname.data = rn->u.cname;
 
-                return ngx_resolve_name_locked(r, ctx);
+                return ngx_resolve_name_locked(r, ctx, &cname);
             }
 
             last->next = rn->waiting;
@@ -592,6 +591,11 @@ ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
             rn->waiting = ctx;
             ctx->state = NGX_AGAIN;
 
+            do {
+                ctx->node = rn;
+                ctx = ctx->next;
+            } while (ctx);
+
             return NGX_AGAIN;
         }
 
@@ -630,14 +634,14 @@ ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
             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;
@@ -646,7 +650,7 @@ ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
         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;
@@ -710,6 +714,11 @@ ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
 
     ctx->state = NGX_AGAIN;
 
+    do {
+        ctx->node = rn;
+        ctx = ctx->next;
+    } while (ctx);
+
     return NGX_AGAIN;
 
 failed:
@@ -832,6 +841,7 @@ 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 */
 
@@ -917,6 +927,7 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx)
     /* unlock addr mutex */
 
     ctx->state = NGX_AGAIN;
+    ctx->node = rn;
 
     return NGX_OK;
 
@@ -947,17 +958,11 @@ 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;
 
@@ -986,21 +991,7 @@ ngx_resolve_addr_done(ngx_resolver_ctx_t *ctx)
 
     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;
@@ -1989,9 +1980,12 @@ ngx_resolver_process_a(ngx_resolver_t *r, u_char *buf, size_t last,
         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);
diff --git a/src/core/ngx_resolver.h b/src/core/ngx_resolver.h
index 264c8c4..0186e22 100644
--- 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;
 };