[3.13.y-ckt stable] Patch "mm: fix anon_vma_clone() error treatment" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    mm: fix anon_vma_clone() error treatment

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From e27dc77a59d703151279518dfd7bb7e1fec1ab3c Mon Sep 17 00:00:00 2001
From: Daniel Forrest <dan.forrest at ssec.wisc.edu>
Date: Tue, 2 Dec 2014 15:59:42 -0800
Subject: mm: fix anon_vma_clone() error treatment

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 at ssec.wisc.edu>
Reviewed-by: Michal Hocko <mhocko at suse.cz>
Cc: Konstantin Khlebnikov <koct9i at gmail.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: Rik van Riel <riel at redhat.com>
Cc: Tim Hartrick <tim at edgecast.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Michel Lespinasse <walken at google.com>
Cc: Vlastimil Babka <vbabka at suse.cz>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.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 32dbf6d..d407dcd 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -742,8 +742,11 @@ 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;
 		}
 	}
@@ -2414,7 +2417,8 @@ 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 cd6b576..ac0506d 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();
--
1.9.1