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Re: Setting effective UID for a shell script

On  0, "Eric G. Miller" <egm2@jps.net> wrote:
> On Wed, May 15, 2002 at 05:17:41PM +0930, Tom Cook wrote:
> > However, you are not entirely correct.  This does, in fact, compile,
> > with the exception of the type of execve for execv.  It also, funnily
> > enough, doesn't loop infinitely, which makes me think that the execv
> > call is just failing.  I am Interested, but not enough to figure out
> > Why.
> $ gcc -g -Wall -o suidscript suidscript.c
> suidscript.c: In function `main':
> suidscript.c:4: warning: passing arg 2 of `execve' from incompatible
> pointer type
> suidscript.c:4: too few arguments to function `execve'
> $ ls suidscript
> ls: suidscript: No such file or directory

You didn't fix the typo I pointed out.

> Note: I said "semantically", since you pass argv[0] as the command to
> execute, the program will keep executing itself (if argv[0] is fully
> qualified).  But, if you managed to get it to compile, it no doubt is
> segfaulting due to noted errors above.

It compiles fine for me (after the typo is corrected).  You are
correct, the call should be:

   execv( argv[1], argv[2] );

For the fanatically correct, this might be better:

   execv( argv[1], argv + sizeof( argv[1] ) );

but the effect is the same (in fact the generated code is probably the

As I mentioned, though, it doesn't loop indefinitely, even when you
try to execv argv[0] - it just exits.  No segfault.  No indefinite

Tom Cook
Information Technology Services, The University of Adelaide

"A child of five could understand this.  Fetch me a child of five."
	- Groucho Marx

Get my GPG public key: https://pinky.its.adelaide.edu.au/~tkcook/tom.cook-at-adelaide.edu.au

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