Messages in this thread | | | Date | Mon, 21 Mar 2022 13:12:00 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH v2] mm/mempolicy: fix mpol_new leak in shared_policy_replace |
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On Tue 22-03-22 16:34:56, Miaohe Lin wrote: > If mpol_new is allocated but not used in restart loop, mpol_new will be > freed via mpol_put before returning to the caller. But refcnt is not > initialized yet, so mpol_put could not do the right things and might leak > the unused mpol_new.
I would just add:
This would happen if mempolicy was updated on the shared shmem file while the sp->lock has been dropped during the memory allocation.
> This issue could be triggered easily with the below > code snippet if there're many processes doing the below work at the same > time: > > shmid = shmget((key_t)5566, 1024 * PAGE_SIZE, 0666|IPC_CREAT); > shm = shmat(shmid, 0, 0); > loop many times { > mbind(shm, 1024 * PAGE_SIZE, MPOL_LOCAL, mask, maxnode, 0); > mbind(shm + 128 * PAGE_SIZE, 128 * PAGE_SIZE, MPOL_DEFAULT, mask, > maxnode, 0); > } > > Fixes: 42288fe366c4 ("mm: mempolicy: Convert shared_policy mutex to spinlock") > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > Cc: <stable@vger.kernel.org> # 3.8
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks a lot! > --- > v1->v2: > Add reproducer snippet and Cc stable. > Thanks Michal Hocko for review and comment! > --- > mm/mempolicy.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index a2516d31db6c..4cdd425b2752 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -2733,6 +2733,7 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start, > mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL); > if (!mpol_new) > goto err_out; > + refcount_set(&mpol_new->refcnt, 1); > goto restart; > } > > -- > 2.23.0
-- Michal Hocko SUSE Labs
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