Monday, October 21, 2013

Git and Bit Errors

Finally, a topic to unite my two most popular blog posts: git failures and bitsquatting.

A friend recently pointed me to an amazingly detailed investigation of a corrupted git repository. The cause of the corruption? A single bit flip. To quote the source:

As for the corruption itself, I was lucky that it was indeed a single
byte. In fact, it turned out to be a single bit. The byte 0xc7 was
corrupted to 0xc5. So presumably it was caused by faulty hardware, or a
cosmic ray.
And the aborted attempt to look at the inflated output to see what was
wrong? I could have looked forever and never found it. Here's the diff
between what the corrupted data inflates to, versus the real data:
  -       cp = strtok (arg, "+");
  +       cp = strtok (arg, ".");

It is quite amazing to see evidence of a bit error resulting in a perfectly innocuous, syntactically valid and yet completely erroneous change in a real program and a real codebase.

How many times does this happen without anyone noticing?

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