[PATCH 3.17 06/47] mm: fix anon_vma_clone() error treatment

From: Greg Kroah-Hartman
Date: Sun Dec 14 2014 - 15:29:31 EST

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


From: Daniel Forrest <dan.forrest@xxxxxxxxxxxxx>

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@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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -752,8 +752,11 @@ 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;
@@ -2453,7 +2456,8 @@ 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)
--- a/mm/rmap.c
+++ b/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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