exec after seteuid

Pierre A. Humblet Pierre.Humblet@ieee.org
Sat Jun 7 19:34:00 GMT 2003

At 09:14 PM 6/7/2003 +0200, Corinna Vinschen wrote:
>> Here is a candidate patch. I don't want to start sinking
>> test time before you have a chance to tell me it won't work,
>> or improve it.
>No, that's an interesting idea.  I would appreciate some testing.
OK, will do. I already saw some small holes, related to
Win9X support and the case where the token changes because 
of groups.

>> If both uids have changed, then we need to build two
>> tokens. That's a big job.
>But that isn't very likely, right?  Most setuid applications are
>either changing the uid for a quick job or they switch over
>entirely to ruid == euid for their unprivileged child processes.

100% OK

>Do you think it's worth to consider such a border case?

Not until someone asks for it!

I was just thinking about the security implications. For example
login uses seteuid. With the change, the shell would still start
with ruid = 18, and a simple RevertToSelf would bring privileges 
back. I think (all ?) shells setuid(geteuid()), but in Cygwin the 
change wouldn't really be effective until the next exec.
Perhaps it would be safer to have login and such use setuid.


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