tmpfile breakage on setuid executables

[Anoop Ranganath]

The problem reared it's ugly head when maildrop started mishandling
mesasges.  Here is what I've tracked it down to:

I've used the code at the bottom of this message to isolate this
bug.  The summary is that when I compile the code as root, and then
make it setuid (chmod u+s a.out) and then try to run it as a user, the
tmpfile() fails.  If I run it as root, it works fine.  Conversely, I
can give user ownership of the executable, and then run it as user, and
it works great, but if fails for root.  Again this is only with the
setuid bit set.

My system is FreeBSD 5.0-RELEASE (GENERIC) #0: Thu Jan 16 22:16:53 GMT
2003

Thanks,
Anoop

#include <stdlib.h>
#include <stdio.h>

int main( void )
{
     FILE *stream;

     stream = tmpfile();
     if( stream != NULL ) {
         printf( "File number is %d.\n", fileno( stream ) );
         fclose( stream );

         return EXIT_SUCCESS;
     }

     return EXIT_FAILURE;
}



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