57 lines
1.8 KiB
Markdown
57 lines
1.8 KiB
Markdown
# Example Dojo
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This repositories features an example dojo.
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The dojo is defined by [dojo.yml](./dojo.yml).
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It contains two modules, `hello` and `world`.
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The module `hello` features challenges `apple` and `banana`.
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The module `world` features challenges `earth`, `mars`, and `venus`.
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Each challenge demonstrates different challenge definition capabilities, in an increasing order of feature complexity.
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See each challenge's README for further information:
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- [apple](./hello/apple)
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- [banana](./hello/banana)
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- [earth](./world/earth)
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- [mars](./world/mars)
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- [venus](./world/venus)
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## Challenge Writing Laws
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### The Flag
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The flag is located at `/flag`, and is only readable by `root`.
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The challenge will execute as `root`.
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Nothing else is true.
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Do not assume any structure to the flag.
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It may or may not have a prefix/suffix.
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It may or may not be 50 bytes long.
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These things WILL change, and if you rely on them, your challenge WILL break.
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### The Challenge
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The challenge is [`setuid`](https://en.wikipedia.org/wiki/Setuid).
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This is how your challenge will execute as `root`.
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What this *really* means:
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- The process will run with an **effective** user of `root`.
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- The process will run with a **real** user of `hacker`.
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While an **effective** user of `root` is sufficient for opening the flag, there are some caveats.
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When `/bin/sh` (which is linked to `/bin/dash`) is run under this, it will immediately set the **effective** user to the **real** user (unless the `-p` flag is provided).
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This means that both the **effective** and **real** user will be `hacker`, and the flag will not be accessible.
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This affects `system`, which ultimately just runs `/bin/sh`.
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The challenge can rememedy this by explicitly setting the **real** user to the **effective** user:
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```c
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setreuid(geteuid(), -1)
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```
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