Some time ago while in a conversation in IRC, one user in a channel I was in suggested someone setuid a directory in order for it to inherit the userid on files to solve a problem someone else was having. At the time I spoke up and said "linux doesn't support setuid directories". After that, the person giving the advice showed me a pastebin (http://codepad.org/4In62f13) of his system honouring the setuid permission set on a directory.
Just to explain, when i say "linux doesnt support setuid directories" what I mean is that you can go "chmod u+s directory" and it will set the bit on the directory. However, linux (as i understood it) ignores this bit (on directories).
Try as I might, I just cant quite replicate that pastebin. Someone suggested to me once that it might be possible to emulate the behaviour with selinux – and playing around with rules, its possible to force a uid on a file, but not from a setuid directory permission (that I can see). Reading around on the internet has been fairly uninformative – most places claim "no, setuid on directories does not work with linux" with the occasional "it can be done under specific circumstances" (such as this: http://arstechnica.com/etc/linux/2003/linux.ars-12032003.html)
I dont remember who the original person was, but the original system was a debian 6 system, and the filesystem it was running was xfs mounted with "default,acl". I've tried replicating that, but no luck so far (tried so far with various versions of debian, ubuntu, fedora and centos)
Can anyone clue me in on what or how you get a system to honor setuid on a directory?
Best Answer
Setuid for directories does not behave like setgid. Unless, the shell output was from FreeBSD, some one was bored and having a little fun at your expense.
http://en.wikipedia.org/wiki/Setuid#setuid_and_setgid_on_directories