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    Subject[PATCH 3.16.y-ckt 146/168] mm: fix anon_vma_clone() error treatment
    Date
    3.16.7-ckt3 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Daniel Forrest <dan.forrest@ssec.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@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>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Luis Henriques <luis.henriques@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 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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