[Live-devel] Fix for a possible buffer overflow in SDESItem

[Jeremy Noring]

In RTCP.cpp,

SDESItem::SDESItem(unsigned char tag, unsigned char const* value) {
  unsigned length = strlen((char const*)value);
  if (length > 511) length = 511;

  fData[0] = tag;
  fData[1] = (unsigned char)length;
  memmove(&fData[2], value, length);

  // Pad the trailing bytes to a 4-byte boundary:
  while ((length)%4 > 0) fData[2 + length++] = '\0';
}

length is 511 bytes, and the additional padding at the end tacks on up to 3
more bytes.  However, the buffer to which memory is being written to in
RTCP.hh is declared as:

unsigned char fData[2 + 0xFF]; // first 2 bytes are tag and length

...which is only 257 bytes.  It needs to be at least 515 bytes in length
(511+ 2 is 513; padded to before the nearest 4 byte boundary bumps that up
to 515).  So that line should change to:

unsigned char fData[2 + 513]; // first 2 bytes are tag and length

Either that, or the upper bound on "length" in the constructor needs to be
shortened. (to work with 2 + 0xFF, length would need to be no greater than
251)

Thanks,

Jeremy
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