Messages in this thread | | | Date | Fri, 07 Sep 2012 19:06:57 -0400 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() |
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> mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() > > [cc9a6c87: cpuset: mm: reduce large amounts of memory barrier related damage > v3] introduced a potential memory corruption. shmem_alloc_page() uses a > pseudo vma and it has one significant unique combination, vma->vm_ops=NULL > and vma->policy->flags & MPOL_F_SHARED. > > get_vma_policy() does NOT increase a policy ref when vma->vm_ops=NULL and > mpol_cond_put() DOES decrease a policy ref when a policy has MPOL_F_SHARED. > Therefore, when a cpuset update race occurs, alloc_pages_vma() falls in 'goto > retry_cpuset' path, decrements the reference count and frees the policy > prematurely. > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > Signed-off-by: Mel Gorman <mgorman@suse.de> > --- > mm/mempolicy.c | 12 +++++++++++- > 1 files changed, 11 insertions(+), 1 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 45f9825..9842ef5 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task, > addr); > if (vpol) > pol = vpol; > - } else if (vma->vm_policy) > + } else if (vma->vm_policy) { > pol = vma->vm_policy; > + > + /* > + * shmem_alloc_page() passes MPOL_F_SHARED policy with > + * a pseudo vma whose vma->vm_ops=NULL. Take a reference > + * count on these policies which will be dropped by > + * mpol_cond_put() later > + */ > + if (mpol_needs_cond_ref(pol)) > + mpol_get(pol); > + }
Ok, looks sene change. thank you.
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> } > if (!pol) > pol = &default_policy; >
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