Recovering chmod's execute permission

Question

This was an interview question. Let's say you revoked the execute permission of chmod binary -- i.e., you cannot run "chmod u+x chmod" because chmod doesn't have +x. Without obtaining a copy of chmod's binary file outside of the local file system, how can you recover chmod's execute permission?

Answer 1

1) Use install:

install -m +rx /bin/chmod /tmp/chmod
/tmp/chmod 755 /bin/chmod # or just copy it back.

2) Use busybox's chmod

/bin/busybox chmod 755 /bin/chmod

3) Use cp and cat (dd can work as well):

cp -a /bin/sh /tmp/chmod
cat /bin/chmod > /tmp/chmod
/tmp/chmod 755 /bin/chmod