Hi,
I have a script that needs to find out where it was executed from. The following script:
#!/usr/bin/perl -w
print "$0\n";
normally works ok. However, if the script is set-uid
(to any user) it prints something like "/dev/fd/3". This
is under Solaris 2.7. The FindBin modules uses $0 as its
starting point, so it doesn't work either.
I read somewhere that this is a trick used by some
kernels to safely execute set-uid scripts: when a set-uid
script is invoked, the kernel passes the script to the
interpreter using a file descriptor instead of the file
name directly, to avoid race conditions. If this is the case,
my problem may be unsolvable, but I thought I would ask
anyway.
I asked in comp.lang.perl.misc about this, and got two main
suggestions, which I list with their drawbacks:
- Have a non-suid wrapper script that gets the program
path, stores in in an environment variable and then executes
the suid script. Drawback: anyone can set the environment
variable and execute the suid script directly.
- Have a "helper" non-suid script that prints its path
to stdout, and that is stored in the same directory as the
suid script. Then the suid script can use it to find out
its path. Drawback: the directory where both scripts are
stored has to be in the user's path.
So I'm still looking for a real answer to my question.
Any ideas will be very appreciated!
Thanks,
--Diego
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