Bug 3043

in 2.6.x and 2.4.x kernels, if a core file owned by a non root user exists and 
root runs a process that drops core in the same location, the original core 
file owned by the non root user is replaced with root's core dump, except the 
original owner maintains ownership of the core.  obsd and fbsd operate in the 
same manner.  i have not tested other platforms

trew@uber:~/tmp/q$ ./t
Segmentation fault (core dumped)
trew@uber:~/tmp/q$ md5sum core
90b29a1012aa00c34a18947d98f1b1fb  core
trew@uber:~/tmp/q$ ls -l core
-rw-------    1 trew     users       61440 Jul 10 19:13 core
trew@uber:~/tmp/q$ su
Password:
uber:/home/trew/tmp/q# ./t
Segmentation fault (core dumped)
uber:/home/trew/tmp/q# md5sum core
371c0748df009ed1da6f189cceff8aca  core
uber:/home/trew/tmp/q# ls -l core
-rw-------    1 trew     users       61440 Jul 10 19:13 core