From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id B5C356B0003 for ; Sun, 8 Apr 2018 22:49:29 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id p10so4302996pfl.22 for ; Sun, 08 Apr 2018 19:49:29 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id g4si11944379pfm.358.2018.04.08.19.49.28 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 08 Apr 2018 19:49:28 -0700 (PDT) Date: Sun, 8 Apr 2018 19:49:25 -0700 From: Matthew Wilcox Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference Message-ID: <20180409024925.GA21889@bombadil.infradead.org> References: <20180409015815.235943-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180409015815.235943-1-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries On Mon, Apr 09, 2018 at 10:58:15AM +0900, Minchan Kim wrote: > It assumes shadow entry of radix tree relies on the init state > that node->private_list allocated should be list_empty state. > Currently, it's initailized in SLAB constructor which means > node of radix tree would be initialized only when *slub allocates > new page*, not *new object*. So, if some FS or subsystem pass > gfp_mask to __GFP_ZERO, slub allocator will do memset blindly. Wait, what? Who's declaring their radix tree with GFP_ZERO flags? I don't see anyone using INIT_RADIX_TREE or RADIX_TREE or RADIX_TREE_INIT with GFP_ZERO. Although, even if nobody's doing that intentionally, if somebody has a bitflip with the __GFP_ZERO bit, it's going to propagate widely. I think something like this might be appropriate: diff --git a/mm/slub.c b/mm/slub.c index 9e1100f9298f..0f55f0a0dcaa 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2714,8 +2714,10 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, stat(s, ALLOC_FASTPATH); } - if (unlikely(gfpflags & __GFP_ZERO) && object) - memset(object, 0, s->object_size); + if (unlikely(gfpflags & __GFP_ZERO) && object) { + if (!WARN_ON_ONCE(s->ctor)) + memset(object, 0, s->object_size); + } slab_post_alloc_hook(s, gfpflags, 1, &object); Something you could try is checking that the list is empty when the node is inserted into the radix tree. diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 8e00138d593f..580f52d0c072 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -428,6 +428,7 @@ radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent, ret->exceptional = exceptional; ret->parent = parent; ret->root = root; + BUG_ON(!list_empty(&ret->private_list)); } return ret; }