perl executes mode 0 argument passed script when called through sudo, security hole?

[Don Coyote]

This may not be a perl specific thing. But I was not sure and thought best to mention in case. I call a chmod 0 script by itself and by perl in my user shell (bash). And fails as expected. I set-uid and still fails which I think is right as mode is 4000.

Now I set mode back to 0 and pass the script in as an argument to perl, in my user environment this fails, but under sudo the script executes.

I am not sure but is this working properly? being mode 0 I would have thought the script would not be executable whether or not set-uid. I have included most of my dabbling for reference, the interesting calls are closer to the bottom of the script.

$ login

Ubuntu LTS 10.04.4

263 updates avaliable
238 are security updates

hilarious@hilarious-desktop:~/Documents$ perl -v

This is perl, v5.10.1 (*) built for x86_64-linux-gnu-thread-multi

hilarious@hilarious-desktop:~/Documents$ mkdir ./messin
$ cd ./messin
$ touch ./hmm
$ ls
hmm
$ ls -l ./hmm
-rw------- 1 hilarious hilarious 0 2013-11-10 17:36 ./hmm
$ chmod 0200 ./hmm
$ ls -l ./hmm
--w------- 1 hilarious hilarious 0 2013-11-10 17:36 ./hmm
$ emacs ./hmm
$ emacs -nw ./hmm
$ emacs -nw ./hmm
$ chmod 0000 ./hmm
$ ls -l ./hmm
---------- 1 hilarious hilarious 0 2013-11-10 17:36 ./hmm
$ emacs -nw ./hmm
$ chmod 0200 ./hmm
$ chmod 0400 ./hmm
$ emacs -nw ./hmm
$ chmod 0600 ./hmm
$ emacs -nw ./hmm
$ ls -l ./hmm
-rw------- 1 hilarious hilarious 92 2013-11-10 17:57 ./hmm
$ ./hmm
bash: ./hmm: Permission denied
$ sudo ./hmm
[sudo] password for hilarious:
sudo: ./hmm: command not found
$ su hilarious
Password:
Warning: your password will expire in 4 days
$ who am i
hilarious pts/1        2013-11-10 17:35 (:0.0)
$ ./hmm
Can't open perl script "./hmm": Permission denied
$ chmod 5 ./hmm
$ ./hmm
bash: ./hmm: Permission denied
$ ls -l ./hmm
-------r-x 1 hilarious hilarious 92 2013-11-10 17:57 ./hmm
$ chmod 500 ./hmm
$ ./hmm
hello world!
$ chmod 005 ./hmm
$ ./hmm
bash: ./hmm: Permission denied
$ sudo ./hmm
hello world!
$ who am i
hilarious pts/1        2013-11-10 17:35 (:0.0)
$ sudo who am i
hilarious pts/1        2013-11-10 17:35 (:0.0)
$ cmod 007 ./hmm
No command 'cmod' found, did you mean:
 Command 'qmod' from package 'gridengine-client' (universe)
 Command 'chmod' from package 'coreutils' (main)
 Command 'mod' from package 'monodoc-base' (main)
cmod: command not found
$ chmod 007 ./hmm
$ emacs -nw ./hmm
$ ./hmm
bash: ./hmm: Permission denied
$ sudo ./hmm
hello world!
$ chmod 0 ./hmm
$ sudo ./hmm
sudo: ./hmm: command not found
$ sudo perl ./hmm
hello world!
$ perl ./hmm
Can't open perl script "./hmm": Permission denied
$ ls -l ./hmm
---------- 1 hilarious hilarious 92 2013-11-10 17:57 ./hmm
$ chmod 4000 ./hmm
$ ./hmm
bash: ./hmm: Permission denied
$ perl ./hmm
Can't open perl script "./hmm": Permission denied
$ sudo perl ./hmm
Args must match #! line at ./hmm line 1.
$ sudo perl -l ./hmm
Effective UID cannot exec script
$ sudo chmod 0 ./hmm
$ sudo perl ./hmm
hello world!