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Fixed unpacking multiple names from dns packets when one has multiple compression pointers.

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Currently this will just fail at unpacking the later name due to offsets being invalid.
Also cleaned up the existing code and made unpacking error messages more helpful.
This commit is contained in:
Adam
2012-03-27 19:01:29 -04:00
parent 88fd1da803
commit 31a0e673b2
1 changed files with 36 additions and 26 deletions
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src/dns.cpp
+36 -26
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@@ -144,44 +144,54 @@ void DNSPacket::PackName(unsigned char *output, unsigned short output_size, unsi
Anope::string DNSPacket::UnpackName(const unsigned char *input, unsigned short input_size, unsigned short &pos)
{
Anope::string name;
unsigned short pos_ptr = pos;
unsigned short pos_ptr = pos, lowest_ptr = input_size;
bool compressed = false;
if (pos_ptr >= input_size)
throw SocketException("Unable to unpack name");
throw SocketException("Unable to unpack name - no input");
unsigned short offset;
do
while (input[pos_ptr] > 0)
{
offset = input[pos_ptr];
unsigned short offset = input[pos_ptr];
if (offset & DNS_POINTER)
{
if ((offset & DNS_POINTER) != DNS_POINTER)
throw SocketException("Unable to unpack name - bogus compression header");
if (pos_ptr + 1 >= input_size)
throw SocketException("Unable to unpack name");
offset = (offset & DNS_LABEL) << 8 | input[++pos_ptr];
pos_ptr = offset;
if (pos_ptr >= input_size)
throw SocketException("Unable to unpack name");
offset = input[pos_ptr];
++pos;
throw SocketException("Unable to unpack name - bogus compression header");
/* Place pos at the second byte of the first (farthest) compression pointer */
if (compressed == false)
{
++pos;
compressed = true;
}
pos_ptr = (offset & DNS_LABEL) << 8 | input[pos_ptr + 1];
/* Pointers can only go back */
if (pos_ptr >= lowest_ptr)
throw SocketException("Unable to unpack name - bogus compression pointer");
lowest_ptr = pos_ptr;
}
else
{
if (pos_ptr + offset + 1 >= input_size)
throw SocketException("Unable to unpack name - offset too large");
if (!name.empty())
name += ".";
for (unsigned i = 1; i <= offset; ++i)
name += input[pos_ptr + i];
if (pos_ptr + offset >= input_size)
throw SocketException("Unable to unpack name");
if (!name.empty())
name += ".";
for (unsigned i = 1; i <= offset; ++i)
name += input[pos_ptr + i];
pos_ptr += offset + 1;
if (pos_ptr >= input_size)
throw SocketException("Unable to unpack name");
offset = input[pos_ptr];
if (pos_ptr > pos)
pos = pos_ptr;
pos_ptr += offset + 1;
if (compressed == false)
/* Move up pos */
pos = pos_ptr;
}
}
while (offset);
/* +1 pos either to one byte after the compression pointer or one byte after the ending \0 */
++pos;
Log(LOG_DEBUG_2) << "Resolver: UnpackName successfully unpacked " << name;