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    SubjectRe: NULL-ptr deref in mmput via sys_migrate_pages in 3.4-rc4 (proly missing mm==NULL check)
    Commit 3268c63eded4612a3d07b56d1e02ce7731e6608e introduced two potential NULL dereferences.
    Move the mmput calls into the if arms that have already tested for a valid mm.

    Reported-by: Robert Święcki <robert@swiecki.net>
    Cc: Christoph Lameter <cl@linux.com>
    Signed-off-by: Dave Jones <davej@redhat.com>

    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index cfb6c86..6de4850 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -1361,13 +1361,12 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,

    mm = get_task_mm(task);
    put_task_struct(task);
    - if (mm)
    + if (mm) {
    err = do_migrate_pages(mm, old, new,
    capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
    - else
    + mmput(mm);
    + } else
    err = -EINVAL;
    -
    - mmput(mm);
    out:
    NODEMASK_SCRATCH_FREE(scratch);

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 51c08a0..d73d860 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -1389,15 +1389,15 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
    put_task_struct(task);

    if (mm) {
    - if (nodes)
    + if (nodes) {
    err = do_pages_move(mm, task_nodes, nr_pages, pages,
    nodes, status, flags);
    - else
    + mmput(mm);
    + } else
    err = do_pages_stat(mm, nr_pages, pages, status);
    } else
    err = -EINVAL;

    - mmput(mm);
    return err;

    out:
    --
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