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@ssec.wisc.edu>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tim Hartrick <tim@edgecast.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>	[3.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 87e82b3..ae91989 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -776,8 +776,11 @@ 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;
                }
        }
@@ -2469,7 +2472,8 @@ 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 19886fb..3e4c721 100644 (file)
--- 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();