diff mbox series

[4.19,316/338] mm/mempolicy: fix mpol_new leak in shared_policy_replace

Message ID 20220414110847.881434205@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg KH April 14, 2022, 1:13 p.m. UTC 
From: Miaohe Lin <linmiaohe@huawei.com>

commit 4ad099559b00ac01c3726e5c95dc3108ef47d03e upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/mempolicy.c |    1 +
 1 file changed, 1 insertion(+)
diff mbox series

Patch

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2563,6 +2563,7 @@  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;
 }