Correct git_revparse_single and add revparse fuzzing
#6730
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Many fuzzers will need to operate with a repository; extract the repository initialization from downloads_refs_fuzzer.c into its own utility area.
If there are no caps, don't try to advance past the first NULL to look for object-format. This prevents a possible out-of-bounds read.
When parsing a revspec that ends with a trailing `@`, explicitly stop parsing. Introduce a sentinel variable to explicitly stop parsing. Prior to this, we would set `spec` to `HEAD`, but were looping on the value of `spec[pos]`, so we would continue walking the (new) `spec` at offset `pos`, looking for a NUL. This is obviously an out-of-bounds read. Credit to Michael Rodler (@f0rki) and Amazon AWS Security.
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Introduce address sanitization during builds. Surprisingly, although we enabled various sanitizers (thread, memory, undefinedbehavior) we did not have address sanitizer running. Add that.
Address sanitizer correctly detected a failure to correctly parse capabilities in a first pkt. In our test corpus we have a message with no capabilities (the length of the message is the ref advertisement plus a trailing NUL). We walk off the end of that string trying to read capabilities. Now we honor the
lenbefore checking for caps.Update revparse to correctly stop parsing
specwhen we find a trailing@. Thanks to the Amazon AWS Security team for finding and responsibly disclosing this.