MIPS: Fix bounds check virt_addr_valid

The bounds check used the uninitialized variable vaddr, it should use
the given parameter kaddr instead. When using the uninitialized value
the compiler assumed it to be 0 and optimized this function to just
return 0 in all cases.

This should make the function check the range of the given address and
only do the page map check in case it is in the expected range of
virtual addresses.

Fixes: 074a1e11 ("MIPS: Bounds check virt_addr_valid")
Cc: stable@vger.kernel.org # v4.12+
Cc: Paul Burton <paul.burton@mips.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: f4bug@amsat.org
Cc: linux-mips@vger.kernel.org
Cc: ysu@wavecomp.com
Cc: jcristau@debian.org

arch/mips/mm/mmap.c

@@ -203,7 +203,7 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 
 bool __virt_addr_valid(const volatile void *kaddr)
 {
-	unsigned long vaddr = (unsigned long)vaddr;
+	unsigned long vaddr = (unsigned long)kaddr;
 
 	if ((vaddr < PAGE_OFFSET) || (vaddr >= MAP_BASE))
 		return false;