Basic setuid question

[Scott Dunbar <scott@xigole.com>]

Hi,
I'm trying to implement the suggestions from 
http://subversion.tigris.org/faq.html#website-auto-update to allow me to 
update code via a web interface.  My code is a bit different from the 
example as the example wasn't even trying to work.  The code I'm using 
is below.  However, it appears that the code that is execl()'d is still 
not running as the user I'd like.  The executable created from the code 
below is set to 4755 permissions but it doesn't seem to matter.  I've 
also tried a variety of the set*uid() methods with various failures.  
The printf()'s indicate what I'd expect but the execl()'d program is 
still apparently not running as the correct user.

I'm running on

Linux habanero.xigole.com 2.6.18-6-amd64 #1 SMP Tue Aug 19 04:30:56 UTC 
2008 x86_64 GNU/Linux

and

$ cat /etc/debian_version
4.0

Is there something obvious going on to prevent the execl()'d process 
from running as the correct user?  An strace shows that, in this case, 
the svn command is still accessing information from the original user's 
home account.

Thanks for any help.

Code I'm using:

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
int main( int argc, char** argv )
{
   if( argc != 2 )
   {
       fprintf( stderr, "usage: %s <dir_to_update>\n", argv[0] );
       return(EXIT_FAILURE);
   }

   printf( "(1) euid is %d, uid is %d\n", geteuid(), getuid() );

   if( setreuid(geteuid(), geteuid()) != 0 )
   {
       fprintf( stderr, "Cannot change users.  Reason: %s\n", 
strerror(errno) );
       return(EXIT_FAILURE);
   }

   printf( "(2) euid is %d, uid is %d\n", geteuid(), getuid() );

   execl("/usr/local/bin/svn", "svn", "update", argv[1], (const char *) 
NULL);

   return(EXIT_FAILURE);
}