Commit 287d97ac authored by Linus Torvalds's avatar Linus Torvalds
Browse files

vma_adjust: fix the copying of anon_vma chains 



When we move the boundaries between two vma's due to things like
mprotect, we need to make sure that the anon_vma of the pages that got
moved from one vma to another gets properly copied around.  And that was
not always the case, in this rather hard-to-follow code sequence.

Clarify the code, and fix it so that it copies the anon_vma from the
right source.

Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Tested-by: Borislav Petkov <bp@alien8.de> [ "Yeah, not so much this one either" ]
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d0e9fe17

mm/mmap.c

+8 −16
Original line number Diff line number Diff line
@@ -507,11 +507,12 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start, 
	struct address_space *mapping = NULL;

	struct prio_tree_root *root = NULL;

	struct file *file = vma->vm_file;

	struct anon_vma *anon_vma = NULL;

	long adjust_next = 0;

	int remove_next = 0;



	if (next && !insert) {

		struct vm_area_struct *exporter = NULL;



		if (end >= next->vm_end) {

			/*

			 * vma expands, overlapping all the next, and
@@ -519,7 +520,7 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start, 
			 */

again:			remove_next = 1 + (end > next->vm_end);

			end = next->vm_end;

			anon_vma = next->anon_vma;

			exporter = next;

			importer = vma;

		} else if (end > next->vm_start) {

			/*
@@ -527,7 +528,7 @@ again: remove_next = 1 + (end > next->vm_end); 
			 * mprotect case 5 shifting the boundary up.

			 */

			adjust_next = (end - next->vm_start) >> PAGE_SHIFT;

			anon_vma = next->anon_vma;

			exporter = next;

			importer = vma;

		} else if (end < vma->vm_end) {

			/*
@@ -536,28 +537,19 @@ again: remove_next = 1 + (end > next->vm_end); 
			 * mprotect case 4 shifting the boundary down.

			 */

			adjust_next = - ((vma->vm_end - end) >> PAGE_SHIFT);

			anon_vma = next->anon_vma;

			exporter = vma;

			importer = next;

		}

	}



	/*

	 * When changing only vma->vm_end, we don't really need anon_vma lock.

	 */

	if (vma->anon_vma && (insert || importer || start != vma->vm_start))

		anon_vma = vma->anon_vma;

	if (anon_vma) {

		/*

		 * Easily overlooked: when mprotect shifts the boundary,

		 * make sure the expanding vma has anon_vma set if the

		 * shrinking vma had, to cover any anon pages imported.

		 */

		if (importer && !importer->anon_vma) {

			/* Block reverse map lookups until things are set up. */

			if (anon_vma_clone(importer, vma)) {

		if (exporter && exporter->anon_vma && !importer->anon_vma) {

			if (anon_vma_clone(importer, exporter))

				return -ENOMEM;

			}

			importer->anon_vma = anon_vma;

			importer->anon_vma = exporter->anon_vma;

		}

	}

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