linux-kernel - [PATCH 3.16.y-ckt 146/168] mm: fix anon_vma

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Message-Id: <1418653622-21105-147-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 15 Dec 2014 14:26:40 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Daniel Forrest <dan.forrest@...c.wisc.edu>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Tim Hartrick <tim@...ecast.com>,
	Hugh Dickins <hughd@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 146/168] mm: fix anon_vma_clone() error treatment

3.16.7-ckt3 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Forrest <dan.forrest@...c.wisc.edu>

commit c4ea95d7cd08d9ffd7fa75e6c5e0332d596dd11e upstream.

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@...c.wisc.edu>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Cc: Konstantin Khlebnikov <koct9i@...il.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Tim Hartrick <tim@...ecast.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Michel Lespinasse <walken@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 mm/mmap.c | 10 +++++++---
 mm/rmap.c |  6 ++++--
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 874e0e5ea193..4813ecec5a94 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -747,8 +747,11 @@ again:			remove_next = 1 + (end > next->vm_end);
 		 * 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;
 		}
 	}
@@ -2430,7 +2433,8 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 	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 --git a/mm/rmap.c b/mm/rmap.c
index 22a4a7699cdb..78274432b48f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -274,6 +274,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
 {
 	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 *vma, struct vm_area_struct *pvma)
 	 * 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();
-- 
2.1.3

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