diff mbox series

[6/9] mm/mempolicy: fix mpol_new leak in shared_policy_replace

Message ID 20220408200908.9C9E9C385A3@smtp.kernel.org (mailing list archive)
State New
Headers show
Series [1/9] mm: migrate: use thp_order instead of HPAGE_PMD_ORDER for new page allocation. | expand

Commit Message

Andrew Morton April 8, 2022, 8:09 p.m. UTC 
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: 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: 42288fe366c4 ("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>
---

 mm/mempolicy.c |    1 +
 1 file changed, 1 insertion(+)
diff mbox series

Patch

--- a/mm/mempolicy.c~mm-mempolicy-fix-mpol_new-leak-in-shared_policy_replace
+++ a/mm/mempolicy.c
@@ -2733,6 +2733,7 @@  alloc_new:
 	mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL);
 	if (!mpol_new)
 		goto err_out;
+	atomic_set(&mpol_new->refcnt, 1);
 	goto restart;
 }