From 4bde615c5fa2a6a6f61ca533e46a062691d83f45 Mon Sep 17 00:00:00 2001

From: bradh352 <brad@brad-house.com>

Date: Fri, 11 Jun 2021 11:27:45 -0400

Subject: [PATCH 1/2] ares_expand_name() should escape more characters

RFC1035 5.1 specifies some reserved characters and escaping sequences

that are allowed to be specified.  Expand the list of reserved characters

and also escape non-printable characters using the \DDD format as

specified in the RFC.

Bug Reported By: philipp.jeitner@sit.fraunhofer.de

Fix By: Brad House (@bradh352)

---

 ares_expand_name.c | 41 ++++++++++++++++++++++++++++++++++++++---

 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/ares_expand_name.c b/ares_expand_name.c

index 3a38e67..8604543 100644

--- a/ares_expand_name.c

+++ b/ares_expand_name.c

@@ -38,6 +38,26 @@

 static int name_length(const unsigned char *encoded, const unsigned char *abuf,

                        int alen);

+/* Reserved characters for names that need to be escaped */

+static int is_reservedch(int ch)

+{

+  switch (ch) {

+    case '"':

+    case '.':

+    case ';':

+    case '\\':

+    case '(':

+    case ')':

+    case '@':

+    case '$':

+      return 1;

+    default:

+      break;

+  }

+

+  return 0;

+}

+

 /* Expand an RFC1035-encoded domain name given by encoded.  The

  * containing message is given by abuf and alen.  The result given by

  * *s, which is set to a NUL-terminated allocated buffer.  *enclen is

@@ -117,9 +137,18 @@ int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,

           p++;

           while (len--)

             {

-              if (*p == '.' || *p == '\\')

+              if (!isprint(*p)) {

+                /* Output as \DDD for consistency with RFC1035 5.1 */

+                *q++ = '\\';

+                *q++ = '0' + *p / 100;

+                *q++ = '0' + (*p % 100) / 10;

+                *q++ = '0' + (*p % 10);

+              } else if (is_reservedch(*p)) {

                 *q++ = '\\';

-              *q++ = *p;

+                *q++ = *p;

+              } else {

+                *q++ = *p;

+              }

               p++;

             }

           *q++ = '.';

@@ -177,7 +206,13 @@ static int name_length(const unsigned char *encoded, const unsigned char *abuf,

           encoded++;

           while (offset--)

             {

-              n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;

+              if (!isprint(*encoded)) {

+                n += 4;

+              } else if (is_reservedch(*encoded)) {

+                n += 2;

+              } else {

+                n += 1;

+              }

               encoded++;

             }

           n++;

-- 

2.26.3

From 86cc9241f89c1155111b992ccc03bf76d8ae634a Mon Sep 17 00:00:00 2001

From: bradh352 <brad@brad-house.com>

Date: Fri, 11 Jun 2021 12:39:24 -0400

Subject: [PATCH 2/2] ares_expand_name(): fix formatting and handling of root

 name response

Fixes issue introduced in prior commit with formatting and handling

of parsing a root name response which should not be escaped.

Fix By: Brad House

---

 ares_expand_name.c | 62 ++++++++++++++++++++++++++++++----------------

 1 file changed, 40 insertions(+), 22 deletions(-)

diff --git a/ares_expand_name.c b/ares_expand_name.c

index 8604543..f89ee3f 100644

--- a/ares_expand_name.c

+++ b/ares_expand_name.c

@@ -133,27 +133,37 @@ int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,

         }

       else

         {

-          len = *p;

+          int name_len = *p;

+          len = name_len;

           p++;

+

           while (len--)

             {

-              if (!isprint(*p)) {

-                /* Output as \DDD for consistency with RFC1035 5.1 */

-                *q++ = '\\';

-                *q++ = '0' + *p / 100;

-                *q++ = '0' + (*p % 100) / 10;

-                *q++ = '0' + (*p % 10);

-              } else if (is_reservedch(*p)) {

-                *q++ = '\\';

-                *q++ = *p;

-              } else {

-                *q++ = *p;

-              }

+              /* Output as \DDD for consistency with RFC1035 5.1, except

+               * for the special case of a root name response  */

+              if (!isprint(*p) && !(name_len == 1 && *p == 0))

+                {

+

+                  *q++ = '\\';

+                  *q++ = '0' + *p / 100;

+                  *q++ = '0' + (*p % 100) / 10;

+                  *q++ = '0' + (*p % 10);

+                }

+              else if (is_reservedch(*p))

+                {

+                  *q++ = '\\';

+                  *q++ = *p;

+                }

+              else

+                {

+                  *q++ = *p;

+                }

               p++;

             }

           *q++ = '.';

         }

-    }

+     }

+

   if (!indir)

     *enclen = aresx_uztosl(p + 1U - encoded);

@@ -200,21 +210,29 @@ static int name_length(const unsigned char *encoded, const unsigned char *abuf,

         }

       else if (top == 0x00)

         {

-          offset = *encoded;

+          int name_len = *encoded;

+          offset = name_len;

           if (encoded + offset + 1 >= abuf + alen)

             return -1;

           encoded++;

+

           while (offset--)

             {

-              if (!isprint(*encoded)) {

-                n += 4;

-              } else if (is_reservedch(*encoded)) {

-                n += 2;

-              } else {

-                n += 1;

-              }

+              if (!isprint(*encoded) && !(name_len == 1 && *encoded == 0))

+                {

+                  n += 4;

+                }

+              else if (is_reservedch(*encoded))

+                {

+                  n += 2;

+                }

+              else

+                {

+                  n += 1;

+                }

               encoded++;

             }

+

           n++;

         }

       else

-- 

2.26.3