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)
 ```