From 25f506273b6ae806fd46bfcb6fdaa5b9ec81a05b Mon Sep 17 00:00:00 2001 From: Miaohe Lin Date: Fri, 8 Apr 2022 13:09:07 -0700 Subject: [PATCH] mm/mempolicy: fix mpol_new leak in shared_policy_replace 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 Acked-by: Michal Hocko Cc: KOSAKI Motohiro Cc: Mel Gorman Cc: [3.8] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/mempolicy.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index a52daebcf41ea..d79ab5116a7be 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2559,6 +2559,7 @@ 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; }