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rmap: fix NULL-pointer dereference on THP munlocking

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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: c7ab0d2fdc ("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>
This commit is contained in:
Kirill A. Shutemov 2017-03-09 16:17:20 -08:00 committed by Linus Torvalds
parent c9a1b80dae
commit 8346242a7e
1 changed files with 7 additions and 6 deletions
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13
mm/rmap.c
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@ -1316,12 +1316,6 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
}
while (page_vma_mapped_walk(&pvmw)) {
subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
address = pvmw.address;
/* Unexpected PMD-mapped THP? */
VM_BUG_ON_PAGE(!pvmw.pte, page);
/*
* If the page is mlock()d, we cannot swap it out.
* If it's recently referenced (perhaps page_referenced
@ -1345,6 +1339,13 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
continue;
}
/* Unexpected PMD-mapped THP? */
VM_BUG_ON_PAGE(!pvmw.pte, page);
subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
address = pvmw.address;
if (!(flags & TTU_IGNORE_ACCESS)) {
if (ptep_clear_flush_young_notify(vma, address,
pvmw.pte)) {