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mm: fix regression in remap_file_pages() emulation

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Grazvydas Ignotas has reported a regression in remap_file_pages()
emulation.

Testcase:
	#define _GNU_SOURCE
	#include <assert.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <sys/mman.h>

	#define SIZE    (4096 * 3)

	int main(int argc, char **argv)
	{
		unsigned long *p;
		long i;

		p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
				MAP_SHARED | MAP_ANONYMOUS, -1, 0);
		if (p == MAP_FAILED) {
			perror("mmap");
			return -1;
		}

		for (i = 0; i < SIZE / 4096; i++)
			p[i * 4096 / sizeof(*p)] = i;

		if (remap_file_pages(p, 4096, 0, 1, 0)) {
			perror("remap_file_pages");
			return -1;
		}

		if (remap_file_pages(p, 4096 * 2, 0, 1, 0)) {
			perror("remap_file_pages");
			return -1;
		}

		assert(p[0] == 1);

		munmap(p, SIZE);

		return 0;
	}

The second remap_file_pages() fails with -EINVAL.

The reason is that remap_file_pages() emulation assumes that the target
vma covers whole area we want to over map.  That assumption is broken by
first remap_file_pages() call: it split the area into two vma.

The solution is to check next adjacent vmas, if they map the same file
with the same flags.

Fixes: c8d78c1823 ("mm: replace remap_file_pages() syscall with emulation")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Cc: <stable@vger.kernel.org>	[4.0+]
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 2016-02-17 13:11:15 -08:00 committed by Linus Torvalds
parent 69a8ec2d81
commit 48f7df3294
1 changed files with 29 additions and 5 deletions
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34
mm/mmap.c
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@ -2664,12 +2664,29 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
if (!vma || !(vma->vm_flags & VM_SHARED))
goto out;
if (start < vma->vm_start || start + size > vma->vm_end)
if (start < vma->vm_start)
goto out;
if (pgoff == linear_page_index(vma, start)) {
ret = 0;
goto out;
if (start + size > vma->vm_end) {
struct vm_area_struct *next;
for (next = vma->vm_next; next; next = next->vm_next) {
/* hole between vmas ? */
if (next->vm_start != next->vm_prev->vm_end)
goto out;
if (next->vm_file != vma->vm_file)
goto out;
if (next->vm_flags != vma->vm_flags)
goto out;
if (start + size <= next->vm_end)
break;
}
if (!next)
goto out;
}
prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;
@ -2679,9 +2696,16 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
flags &= MAP_NONBLOCK;
flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
if (vma->vm_flags & VM_LOCKED) {
struct vm_area_struct *tmp;
flags |= MAP_LOCKED;
/* drop PG_Mlocked flag for over-mapped range */
munlock_vma_pages_range(vma, start, start + size);
for (tmp = vma; tmp->vm_start >= start + size;
tmp = tmp->vm_next) {
munlock_vma_pages_range(tmp,
max(tmp->vm_start, start),
min(tmp->vm_end, start + size));
}
}
file = get_file(vma->vm_file);