61 lines
2.1 KiB
Markdown
61 lines
2.1 KiB
Markdown
# hclsyntax fuzzing utilities
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This directory contains helper functions and corpuses that can be used to
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fuzz-test the `hclsyntax` parsers using [go-fuzz](https://github.com/dvyukov/go-fuzz).
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To fuzz, first install go-fuzz and its build tool in your `GOPATH`:
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```
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$ make tools
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```
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Now you can fuzz one or all of the parsers:
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```
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$ make fuzz-config FUZZ_WORK_DIR=/tmp/hcl2-fuzz-config
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$ make fuzz-expr FUZZ_WORK_DIR=/tmp/hcl2-fuzz-expr
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$ make fuzz-template FUZZ_WORK_DIR=/tmp/hcl2-fuzz-template
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$ make fuzz-traversal FUZZ_WORK_DIR=/tmp/hcl2-fuzz-traversal
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```
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In all cases, set `FUZZ_WORK_DIR` to a directory where `go-fuzz` can keep state
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as it works. This should ideally be in a ramdisk for efficiency, and should
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probably _not_ be on an SSD to avoid thrashing it.
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## Understanding the result
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A small number of subdirectories will be created in the work directory.
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If you let `go-fuzz` run for a few minutes (the more minutes the better) it
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may detect "crashers", which are inputs that caused the parser to panic. Details
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about these are written to `$FUZZ_WORK_DIR/crashers`:
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```
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$ ls /tmp/hcl2-fuzz-config/crashers
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7f5e9ec80c89da14b8b0b238ec88969f658f5a2d
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7f5e9ec80c89da14b8b0b238ec88969f658f5a2d.output
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7f5e9ec80c89da14b8b0b238ec88969f658f5a2d.quoted
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```
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The base file above (with no extension) is the input that caused a crash. The
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`.output` file contains the panic stack trace, which you can use as a clue to
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figure out what caused the crash.
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A good first step to fixing a detected crasher is to copy the failing input
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into one of the unit tests in the `hclsyntax` package and see it crash there
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too. After that, it's easy to re-run the test as you try to fix it. The
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file with the `.quoted` extension contains a form of the input that is quoted
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in Go syntax for easy copy-paste into a test case, even if the input contains
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non-printable characters or other inconvenient symbols.
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## Rebuilding for new Upstream Code
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An archive file is created for `go-fuzz` to use on the first run of each
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of the above, as a `.zip` file created in this directory. If upstream code
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is changed these will need to be deleted to cause them to be rebuilt with
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the latest code:
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```
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$ make clean
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```
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