But I think most OSS code isn't like this -- even C code born long ago, if it's still in wide use, has been hardened by now. Examples: Linux kernel, GNU userland, PostgreSQL, Python.
There have been two LPE vulnerability and exploits in the Linux kernel announced today. After the one announced just last week. I don't think as much of the C code born long ago has been as carefully hardened as you think.
(Copy Fail 2 and Dirty Frag today, and Copy Fail last week)
You (anyone, not you personally) write that much code yourself and let's see how well you did in comparison.