drivers: char: mem: Check for address space wraparound with mmap()

drivers: char: mem: Check for address space wraparound with mmap()

/dev/mem currently allows mmap() mappings that wrap around the end of
the physical address space, which should probably be illegal. It
circumvents the existing STRICT_DEVMEM permission check because the loop
immediately terminates (as the start address is already higher than the
end address). On the x86_64 architecture it will then cause a panic
(from the BUG(start >= end) in arch/x86/mm/pat.c:reserve_memtype()).

This patch adds an explicit check to make sure offset + size will not
wrap around in the physical address type.

Signed-off-by: Julius Werner <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>