[patch 08/10] mm: fix anon_vma_clone() error treatment

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From: Daniel Forrest <dan.forrest@xxxxxxxxxxxxx>
Subject: mm: fix anon_vma_clone() error treatment

Andrew Morton noticed that the error return from anon_vma_clone() was
being dropped and replaced with -ENOMEM (which is not itself a bug because
the only error return value from anon_vma_clone() is -ENOMEM).

I did an audit of callers of anon_vma_clone() and discovered an actual bug
where the error return was being lost.  In __split_vma(), between Linux
3.11 and 3.12 the code was changed so the err variable is used before the
call to anon_vma_clone() and the default initial value of -ENOMEM is
overwritten.  So a failure of anon_vma_clone() will return success since
err at this point is now zero.

Below is a patch which fixes this bug and also propagates the error return
value from anon_vma_clone() in all cases.

Fixes: ef0855d334e1 ("mm: mempolicy: turn vma_set_policy() into vma_dup_policy()")
Signed-off-by: Daniel Forrest <dan.forrest@xxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Tim Hartrick <tim@xxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[3.12+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/mmap.c |   10 +++++++---
 mm/rmap.c |    6 ++++--
 2 files changed, 11 insertions(+), 5 deletions(-)

diff -puN mm/mmap.c~mm-fix-anon_vma_clone-error-treatment mm/mmap.c
--- a/mm/mmap.c~mm-fix-anon_vma_clone-error-treatment
+++ a/mm/mmap.c
@@ -776,8 +776,11 @@ again:			remove_next = 1 + (end > next->
 		 * shrinking vma had, to cover any anon pages imported.
 		 */
 		if (exporter && exporter->anon_vma && !importer->anon_vma) {
-			if (anon_vma_clone(importer, exporter))
-				return -ENOMEM;
+			int error;
+
+			error = anon_vma_clone(importer, exporter);
+			if (error)
+				return error;
 			importer->anon_vma = exporter->anon_vma;
 		}
 	}
@@ -2469,7 +2472,8 @@ static int __split_vma(struct mm_struct
 	if (err)
 		goto out_free_vma;
 
-	if (anon_vma_clone(new, vma))
+	err = anon_vma_clone(new, vma);
+	if (err)
 		goto out_free_mpol;
 
 	if (new->vm_file)
diff -puN mm/rmap.c~mm-fix-anon_vma_clone-error-treatment mm/rmap.c
--- a/mm/rmap.c~mm-fix-anon_vma_clone-error-treatment
+++ a/mm/rmap.c
@@ -274,6 +274,7 @@ int anon_vma_fork(struct vm_area_struct
 {
 	struct anon_vma_chain *avc;
 	struct anon_vma *anon_vma;
+	int error;
 
 	/* Don't bother if the parent process has no anon_vma here. */
 	if (!pvma->anon_vma)
@@ -283,8 +284,9 @@ int anon_vma_fork(struct vm_area_struct
 	 * First, attach the new VMA to the parent VMA's anon_vmas,
 	 * so rmap can find non-COWed pages in child processes.
 	 */
-	if (anon_vma_clone(vma, pvma))
-		return -ENOMEM;
+	error = anon_vma_clone(vma, pvma);
+	if (error)
+		return error;
 
 	/* Then add our own anon_vma. */
 	anon_vma = anon_vma_alloc();
_
--
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