Address some security concerns in the cgpt tool.

1. Check for potential integer overflow in sector_bytes * sector_count.
2. Added O_NOFOLLOW to open() call - Is this enough?
3. Passing buffer length to GuidToStr(), PMBRToStr().
4. Use unsigned int in GetEntry() to determine stride.
5. Address conversion between UTF16 and UTF8.

Note: The UTF conversion is complex and troublesome, and needs careful
consideration to get right. For now, I've just forced the interpretation of
the partition name to 7-bit ASCII. That's sufficient for the needs of Chrome
OS, and I can file a new issue to handle UTF correctly.


Running "make runtests" invokes the tests/ script, which checks the behavior and output of the cgpt tool.

Review URL:

Change-Id: I5fd29796d8c929527e0cfbc6d5ccbcdc77502c6b
8 files changed