Lay down the laws of the land

2023-02-17 11:33:05 -07:00
parent 329e56f2db
commit c7ec95a4cf
1 changed files with 37 additions and 1 deletions
@@ -18,3 +18,39 @@ See each challenge's README for further information:
 - [earth](./world/earth)
 - [mars](./world/mars)
 - [venus](./world/venus)
+
+## Challenge Writing Laws
+
+### The Flag
+
+The flag is located at `/flag`, and is only readable by root. 
+The challenge will execute as root.
+Nothing else is true.
+
+Do not assume any structure to the flag. 
+It may or may not have a prefix/suffix. 
+It may or may not be 50 bytes long.
+These things WILL change, and if you rely on them, your challenge WILL break.
+
+### The Challenge
+
+The challenge is [`setuid`](https://en.wikipedia.org/wiki/Setuid).
+This is how your challenge will execute as root.
+
+What this *really* means:
+- The process will run with an **effective** user of `root`.
+- The process will run with a **real** user of `hacker`.
+
+While an **effective** user of `root` is sufficient for opening the flag, there are some caveats.
+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).
+This means that both the **effective** and **real** user will be `hacker`, and the flag will not be accessible.
+This affects `system`, which ultimately just runs `/bin/sh`.
+
+The challenge can rememedy this by explicitly setting the **real** user to the **effective** user:
+```c
+setreuid(geteuid(), -1)
+```
+
+
+
+