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mm/mempolicy: fix mpol_new leak in shared_policy_replace 

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.  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 are 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);
  }

Link: https://lkml.kernel.org/r/20220329111416.27954-1-linmiaohe@huawei.com
Fixes: 42288fe366 ("mm: mempolicy: Convert shared_policy mutex to spinlock")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: <stable@vger.kernel.org>	[3.8]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miaohe Lin 2022-04-08 13:09:07 -07:00 committed by Linus Torvalds
parent 01e67e04c2
commit 4ad099559b
1 changed files with 1 additions and 0 deletions
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mm/mempolicy.c
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@ -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); mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL);
if (!mpol_new) if (!mpol_new)
goto err_out; goto err_out;
atomic_set(&mpol_new->refcnt, 1);
goto restart; goto restart;
} }