rmap: fix NULL-pointer dereference on THP munlocking
authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fri, 10 Mar 2017 00:17:20 +0000 (16:17 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 10 Mar 2017 01:01:10 +0000 (17:01 -0800)
commit8346242a7e32c4c93316684ad8f45473932586b9
tree000c3008bcfb515913ceae12bb7d86cc0d032288
parentc9a1b80daeb50e39f21fd7e62f7224f317ac85f0
rmap: fix NULL-pointer dereference on THP munlocking

The following test case triggers NULL-pointer derefernce in
try_to_unmap_one():

#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>

int main(int argc, char *argv[])
{
int fd;

system("mount -t tmpfs -o huge=always none /mnt");
fd = open("/mnt/test", O_CREAT | O_RDWR);
ftruncate(fd, 2UL << 20);
mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_FIXED | MAP_LOCKED, fd, 0);
mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_LOCKED, fd, 0);
munlockall();
return 0;
}

Apparently, there's a case when we call try_to_unmap() on huge PMDs:
it's TTU_MUNLOCK.

Let's handle this case correctly.

Fixes: c7ab0d2fdc84 ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()")
Link: http://lkml.kernel.org/r/20170302151159.30592-1-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/rmap.c