setuid confusion

[alex at crackpot.org]

Quoting Alex LeDonne <aledonne.listmail at gmail.com>:

> I just found a snippet on
> http://www.linux-knowledge-portal.org/en/content.php?&content/programming/secprog2.html
> :
>
> "The access(2) call uses the real UID and real GID to check the
> rights. This means that the effective UID/GID of SetUID/-GID programs
> does not apply. In the case of the access check with open(2), on the
> other hand, the effective UID/GID is used."
>
> So if svn is using access(2) instead of open(2) to check perms on the
> lock file, your system() call won't work.
>
> I haven't tried to look at subversion source yet to see...
>
> -Alex L

Thanks for the assistance.

I've taken a different approach which is a little clunkier, but also  
works well enough.

The 'wwwlive' user runs a shell script that checks for the presence of  
a flag file.  When that file exists, wwwlive runs an 'svn update' to  
update the live site.  So, anyone who creates that file can cause a  
site update.  Just for safety, I added a wwwlive cron job that checks  
to make sure that shell script is running, and re-starts it if needed.  
  Accomplishes the goal and doesn't require setuid.

alex