# HG changeset patch
# User Ruslan Ermilov <ru@nginx.com>
# Date 1450362076 -10800
# Node ID 33c4d319f08f2b0d33e3fce67852eda10fcc9b33
# Parent  8c8739bdd3f1916b1c010fc0239b76c049580eaa
Resolver: improved PTR response processing.

The previous code only parsed the first answer, without checking its
type, and required a compressed RR name.

The new code checks the RR type, supports responses with multiple
answers, and doesn't require the RR name to be compressed.

This has a side effect in limited support of CNAME.  If a response
includes both CNAME and PTR RRs, like when recursion is enabled on
the server, PTR RR is handled.

Full CNAME support in PTR response is not implemented in this change.

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -2401,7 +2401,7 @@ ngx_resolver_process_ptr(ngx_resolver_t 
     int32_t               ttl;
     ngx_int_t             octet;
     ngx_str_t             name;
-    ngx_uint_t            i, mask, qident, class;
+    ngx_uint_t            mask, type, class, qident, a, i, start;
     ngx_queue_t          *expire_queue;
     ngx_rbtree_t         *tree;
     ngx_resolver_an_t    *an;
@@ -2554,44 +2554,90 @@ valid:
 
     i += sizeof(ngx_resolver_qs_t);
 
-    if (i + 2 + sizeof(ngx_resolver_an_t) >= n) {
+    for (a = 0; a < nan; a++) {
+
+        start = i;
+
+        while (i < n) {
+
+            if (buf[i] & 0xc0) {
+                i += 2;
+                goto found;
+            }
+
+            if (buf[i] == 0) {
+                i++;
+                goto test_length;
+            }
+
+            i += 1 + buf[i];
+        }
+
         goto short_response;
-    }
-
-    /* compression pointer to *.arpa */
-
-    if (buf[i] != 0xc0 || buf[i + 1] != sizeof(ngx_resolver_hdr_t)) {
-        err = "invalid in-addr.arpa or ip6.arpa name in DNS response";
-        goto invalid;
+
+    test_length:
+
+        if (i - start < 2) {
+            err = "invalid name in DNS response";
+            goto invalid;
+        }
+
+    found:
+
+        if (i + sizeof(ngx_resolver_an_t) >= n) {
+            goto short_response;
+        }
+
+        an = (ngx_resolver_an_t *) &buf[i];
+
+        type = (an->type_hi << 8) + an->type_lo;
+        class = (an->class_hi << 8) + an->class_lo;
+        len = (an->len_hi << 8) + an->len_lo;
+        ttl = (an->ttl[0] << 24) + (an->ttl[1] << 16)
+            + (an->ttl[2] << 8) + (an->ttl[3]);
+
+        if (class != 1) {
+            ngx_log_error(r->log_level, r->log, 0,
+                          "unexpected RR class %ui", class);
+            goto failed;
+        }
+
+        if (ttl < 0) {
+            ttl = 0;
+        }
+
+        ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
+                      "resolver qt:%ui cl:%ui len:%uz",
+                      type, class, len);
+
+        i += sizeof(ngx_resolver_an_t);
+
+        switch (type) {
+
+        case NGX_RESOLVE_PTR:
+
+            goto ptr;
+
+        case NGX_RESOLVE_CNAME:
+
+            break;
+
+        default:
+
+            ngx_log_error(r->log_level, r->log, 0,
+                          "unexpected RR type %ui", type);
+        }
+
+        i += len;
     }
 
-    an = (ngx_resolver_an_t *) &buf[i + 2];
-
-    class = (an->class_hi << 8) + an->class_lo;
-    len = (an->len_hi << 8) + an->len_lo;
-    ttl = (an->ttl[0] << 24) + (an->ttl[1] << 16)
-        + (an->ttl[2] << 8) + (an->ttl[3]);
-
-    if (class != 1) {
-        ngx_log_error(r->log_level, r->log, 0,
-                      "unexpected RR class %ui", class);
-        goto failed;
-    }
-
-    if (ttl < 0) {
-        ttl = 0;
-    }
-
-    ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
-                  "resolver qt:%ui cl:%ui len:%uz",
-                  (an->type_hi << 8) + an->type_lo,
-                  class, len);
-
-    i += 2 + sizeof(ngx_resolver_an_t);
-
-    if (i + len > n) {
-        goto short_response;
-    }
+    /* unlock addr mutex */
+
+    ngx_log_error(r->log_level, r->log, 0,
+                  "no PTR type in DNS response");
+    return;
+
+ptr:
 
     if (ngx_resolver_copy(r, &name, buf, buf + i, buf + n) != NGX_OK) {
         goto failed;