When I initially wrote the code for /proc/<pid>/uid_map.  I was lazy
and avoided duplicate mappings by the simple expedient of ensuring the
first number in a new extent was greater than any number in the
previous extent.

Unfortunately that precludes a number of valid mappings, and someone
noticed and complained.  So use a simple check to ensure that ranges
in the mapping extents don't overlap.
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>