Fix boundary check problems in socket_host.cc.

content/browser/renderer_host/p2p/socket_host.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/p2p/socket_host.h"
 
 #include "base/sys_byteorder.h"
 #include "content/browser/renderer_host/p2p/socket_host_tcp.h"
 #include "content/browser/renderer_host/p2p/socket_host_tcp_server.h"
 #include "content/browser/renderer_host/p2p/socket_host_udp.h"
@@ skipping 15 matching lines @@
 const int kAbsSendTimeExtnLen = 3;
 const int kOneByteHdrLen = 1;
 
 // Fake auth tag written by the render process if external authentication is
 // enabled. HMAC in packet will be compared against this value before updating
 // packet with actual HMAC value.
 static const unsigned char kFakeAuthTag[10] = {
     0xba, 0xdd, 0xba, 0xdd, 0xba, 0xdd, 0xba, 0xdd, 0xba, 0xdd
 };
 
-bool IsTurnChannelData(const char* data) {
-  return ((*data & 0xC0) == 0x40);
+bool IsTurnChannelData(const char* data, int len) {

[palmer, 2014/09/22 19:34:46]

size_t, or explicitly-sized unsigned type.

http://www.chromium.org/Home/chromium-security/education/security-tips-for-ip....

[jiayl, 2014/09/22 21:39:02]

Done.

+  return len >= 1 && ((*data & 0xC0) == 0x40);

[palmer, 2014/09/22 19:34:46]

Is there a maximum sane size we should check for, too?

[jiayl, 2014/09/22 21:39:03]

I don't think there is a maximum.

[juberti2, 2014/09/22 22:43:56]

We have a max packet size of 2048 that we use elsewhere. If checking that
provides some extra safety, we should probably do it when the packet is first
received.

[jiayl, 2014/09/22 23:04:13]

Done.

 }
 
 bool IsDtlsPacket(const char* data, int len) {
   const uint8* u = reinterpret_cast<const uint8*>(data);
   return (len >= kDtlsRecordHeaderLen && (u[0] > 19 && u[0] < 64));
 }
 
 bool IsRtcpPacket(const char* data) {
   int type = (static_cast<uint8>(data[1]) & 0x7F);
   return (type >= 64 && type < 96);
 }
 
-bool IsTurnSendIndicationPacket(const char* data) {
+bool IsTurnSendIndicationPacket(const char* data, int len) {
+  if (len < 2)

[palmer, 2014/09/22 19:34:46]

I'd suggest using kMinimumWhateverLength and kMaximumWhateverLength, here and in
|IsTurnChannelData|.

[jiayl, 2014/09/22 21:39:03]

Used the minimum header length for these methods. 

+    return false;
+
   uint16 type = rtc::GetBE16(data);
   return (type == cricket::TURN_SEND_INDICATION);
 }
 
 bool IsRtpPacket(const char* data, int len) {
   return ((*data & 0xC0) == 0x80);
 }
 
 // Verifies rtp header and message length.
 bool ValidateRtpHeader(const char* rtp, int length, size_t* header_length) {
@@ skipping 10 matching lines @@
   // length is verified above.
   if (!(rtp[0] & 0x10)) {
     if (header_length)
       *header_length = rtp_hdr_len_without_extn;
 
     return true;
   }
 
   rtp += rtp_hdr_len_without_extn;
 
+  if (rtp_hdr_len_without_extn + kRtpExtnHdrLen > length) {

[palmer, 2014/09/22 19:34:46]

Integer overflow potential? Consider using checked_numeric<foo> from base/.

[jiayl, 2014/09/22 21:39:02]

The max of the sum is 12 + 4 * 31 + 4 * UINT16_MAX, which should not overflow
size_t.

+    return false;
+  }
+
   // Getting extension profile length.
   // Length is in 32 bit words.
   uint16 extn_length = rtc::GetBE16(rtp + 2) * 4;

[aedla, 2014/09/22 20:06:47]

Would be nice to fix the integer overflow here.

[jiayl, 2014/09/22 21:39:03]

Changed the result to size_t to avoid overflow.

 
   // Verify input length against total header size.
   if (rtp_hdr_len_without_extn + kRtpExtnHdrLen + extn_length > length) {
     return false;
   }
 
   if (header_length)
     *header_length = rtp_hdr_len_without_extn + kRtpExtnHdrLen + extn_length;
   return true;
 }
 
 void UpdateAbsSendTimeExtnValue(char* extn_data, int len,
                                 uint32 abs_send_time) {
   // Absolute send time in RTP streams.
   //
   // The absolute send time is signaled to the receiver in-band using the
   // general mechanism for RTP header extensions [RFC5285]. The payload
   // of this extension (the transmitted value) is a 24-bit unsigned integer
   // containing the sender's current time in seconds as a fixed point number
   // with 18 bits fractional part.
   //
   // The form of the absolute send time extension block:
   //
   //    0                   1                   2                   3
   //    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //   |  ID   | len=2 |              absolute send time               |
   //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-  DCHECK_EQ(len, kAbsSendTimeExtnLen);
+  if (len != kAbsSendTimeExtnLen) {
+    NOTREACHED();
+    return;
+  }
+
   // Now() has resolution ~1-15ms, using HighResNow(). But it is warned not to
   // use it unless necessary, as it is expensive than Now().
   uint32 now_second = abs_send_time;
   if (!now_second) {
     uint64 now_us =
         (base::TimeTicks::HighResNow() - base::TimeTicks()).InMicroseconds();
     // Convert second to 24-bit unsigned with 18 bit fractional part
     now_second =
         ((now_us << 18) / base::Time::kMicrosecondsPerSecond) & 0x00FFFFFF;
   }
   // TODO(mallinath) - Add SetBE24 to byteorder.h in libjingle.
   extn_data[0] = static_cast<uint8>(now_second >> 16);
   extn_data[1] = static_cast<uint8>(now_second >> 8);
   extn_data[2] = static_cast<uint8>(now_second);
 }
 
 // Assumes |len| is actual packet length + tag length. Updates HMAC at end of
 // the RTP packet.
 void UpdateRtpAuthTag(char* rtp, int len,
                       const rtc::PacketOptions& options) {
   // If there is no key, return.
   if (options.packet_time_params.srtp_auth_key.empty())
     return;
 
   size_t tag_length = options.packet_time_params.srtp_auth_tag_len;
   char* auth_tag = rtp + (len - tag_length);

[aedla, 2014/09/22 20:06:47]

Validate tag_length before we create a bad pointer, not after.

[jiayl, 2014/09/22 21:39:03]

Done.

 
   // We should have a fake HMAC value @ auth_tag.
   DCHECK_EQ(0, memcmp(auth_tag, kFakeAuthTag, tag_length));
 
   crypto::HMAC hmac(crypto::HMAC::SHA1);
   if (!hmac.Init(reinterpret_cast<const unsigned char*>(
         &options.packet_time_params.srtp_auth_key[0]),
         options.packet_time_params.srtp_auth_key.size())) {
     NOTREACHED();
     return;
   }
 
-  if (hmac.DigestLength() < tag_length) {
+  const size_t kRocLength = 4;
+
+  if (tag_length > hmac.DigestLength() || tag_length < kRocLength) {

[aedla, 2014/09/22 20:06:47]

That won't cut it. Say tag_length == hmac.DigestLength() == 20 and len == 16.
Then auth_tag == rtp - 4 and second memcpy will OOB write 4 bytes.

Failing with (tag_length > len || tag_length < kRocLength) should be ok from a
security standpoint. Not sure about semantics. I'll think about it a bit more
though.

[jiayl, 2014/09/22 21:39:03]

Done.

     NOTREACHED();
     return;
   }
 
   // Copy ROC after end of rtp packet.
-  memcpy(auth_tag, &options.packet_time_params.srtp_packet_index, 4);
+  memcpy(auth_tag, &options.packet_time_params.srtp_packet_index, kRocLength);
   // Authentication of a RTP packet will have RTP packet + ROC size.
-  int auth_required_length = len - tag_length + 4;
+  int auth_required_length = len - tag_length + kRocLength;

[palmer, 2014/09/22 19:34:46]

Integer overflow potential?

[jiayl, 2014/09/22 21:39:03]

tag_length is guaranteed to be >= kRocLength, so no overflow risk.

 
   unsigned char output[64];
   if (!hmac.Sign(base::StringPiece(rtp, auth_required_length),
                  output, sizeof(output))) {
     NOTREACHED();
     return;
   }
   // Copy HMAC from output to packet. This is required as auth tag length
   // may not be equal to the actual HMAC length.
   memcpy(auth_tag, output, tag_length);
@@ skipping 44 matching lines @@
   }
 
   UpdateRtpAuthTag(start, rtp_length, options);
   return true;
 }
 
 bool GetRtpPacketStartPositionAndLength(const char* packet,
                                         int length,
                                         int* rtp_start_pos,
                                         int* rtp_packet_length) {
+  *rtp_start_pos = 0;
+  *rtp_packet_length = 0;
+
   int rtp_begin;
   int rtp_length = 0;
-  if (IsTurnChannelData(packet)) {
+  if (IsTurnChannelData(packet, length)) {
     // Turn Channel Message header format.
     //   0                   1                   2                   3
     //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     // |         Channel Number        |            Length             |
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     // |                                                               |
     // /                       Application Data                        /
     // /                                                               /
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     if (length < kTurnChannelHdrLen) {
       return false;
     }
 
     rtp_begin = kTurnChannelHdrLen;
     rtp_length = rtc::GetBE16(&packet[2]);
     if (length < rtp_length + kTurnChannelHdrLen) {
       return false;
     }
-  } else if (IsTurnSendIndicationPacket(packet)) {
+  } else if (IsTurnSendIndicationPacket(packet, length)) {
     if (length <= P2PSocketHost::kStunHeaderSize) {
       // Message must be greater than 20 bytes, if it's carrying any payload.
       return false;
     }
     // Validate STUN message length.
     int stun_msg_len = rtc::GetBE16(&packet[2]);
     if (stun_msg_len + P2PSocketHost::kStunHeaderSize != length) {
       return false;
     }
 
@@ skipping 10 matching lines @@
       // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       // |                         Value (variable)                ....
       // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       // The value in the length field MUST contain the length of the Value
       // part of the attribute, prior to padding, measured in bytes.  Since
       // STUN aligns attributes on 32-bit boundaries, attributes whose content
       // is not a multiple of 4 bytes are padded with 1, 2, or 3 bytes of
       // padding so that its value contains a multiple of 4 bytes.  The
       // padding bits are ignored, and may be any value.
       uint16 attr_type, attr_length;
+      const int kAttrHeaderLength = sizeof(attr_type) + sizeof(attr_length);
+
+      if (length < rtp_begin + kAttrHeaderLength) {
+        return false;
+      }
+
       // Getting attribute type and length.
       attr_type = rtc::GetBE16(&packet[rtp_begin]);
       attr_length = rtc::GetBE16(
           &packet[rtp_begin + sizeof(attr_type)]);
+
       // Checking for bogus attribute length.
-      if (length < attr_length + rtp_begin) {
+      if (length < rtp_begin + kAttrHeaderLength + attr_length) {
         return false;
       }
 
       if (attr_type != cricket::STUN_ATTR_DATA) {
         rtp_begin += sizeof(attr_type) + sizeof(attr_length) + attr_length;

[aedla, 2014/09/22 20:06:46]

Use kAttrHeaderLength here.

[jiayl, 2014/09/22 21:39:03]

Done.

         if ((attr_length % 4) != 0) {
           rtp_begin += (4 - (attr_length % 4));
         }
         continue;
       }
 
       data_attr_present = true;
       rtp_begin += 4;  // Skip STUN_DATA_ATTR header.

[aedla, 2014/09/22 20:06:47]

And here.

[jiayl, 2014/09/22 21:39:03]

Done.

       rtp_length = attr_length;
       // One final check of length before exiting.
       if (length < rtp_length + rtp_begin) {

[aedla, 2014/09/22 20:06:47]

This check is now redundant.

[jiayl, 2014/09/22 21:39:02]

Done.

         return false;
       }
       // We found STUN_DATA_ATTR. We can skip parsing rest of the packet.
       break;
     }
 
     if (!data_attr_present) {
       // There is no data attribute present in the message. We can't do anything
       // with the message.
       return false;
@@ skipping 64 matching lines @@
     //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     // |       0xBE    |    0xDE       |           length=3            |
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     // |  ID   | L=0   |     data      |  ID   |  L=1  |   data...
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //       ...data   |    0 (pad)    |    0 (pad)    |  ID   | L=3   |
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     // |                          data                                 |
     // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-    char* extn_start = rtp;
+    const char* extn_start = rtp;

[aedla, 2014/09/22 20:06:46]

Having
const char* extn_end = extn_start + extn_length;
as well would simplify length checks below.

[jiayl, 2014/09/22 21:39:03]

Done.

     while (rtp - extn_start < extn_length) {
       const int id = (*rtp & 0xF0) >> 4;
       const int len = (*rtp & 0x0F) + 1;
+      if (rtp + kOneByteHdrLen + len - extn_start >= extn_length) {

[aedla, 2014/09/22 20:06:48]

I think this should be > extn_length. Or
if (rtp + kOneByteHdrLen + len > extn_end) {

[jiayl, 2014/09/22 21:39:03]

You are right. Done.

+        return false;
+      }
       // The 4-bit length is the number minus one of data bytes of this header
       // extension element following the one-byte header.
       if (id == extension_id) {
         UpdateAbsSendTimeExtnValue(rtp + kOneByteHdrLen, len, abs_send_time);
         found = true;
         break;
       }
       rtp += kOneByteHdrLen + len;
       // Counting padding bytes.
-      while ((*rtp == 0) && (rtp - extn_start < extn_length)) {
+      while ((rtp - extn_start < extn_length) && (*rtp == 0)) {
         ++rtp;
       }
     }
   }
   return found;
 }
 
 }  // packet_processing_helpers
 
 P2PSocketHost::P2PSocketHost(IPC::Sender* message_sender, int socket_id)
@@ skipping 170 matching lines @@
   BrowserThread::PostTask(BrowserThread::UI,
                           FROM_HERE,
                           base::Bind(packet_dump_callback_,
                                      Passed(&packet_header),
                                      header_length,
                                      packet_length,
                                      incoming));
 }
 
 }  // namespace content