From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC407C433F5 for ; Sun, 29 May 2022 23:31:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231808AbiE2Xaj (ORCPT ); Sun, 29 May 2022 19:30:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230417AbiE2Xad (ORCPT ); Sun, 29 May 2022 19:30:33 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 09F20186F1; Sun, 29 May 2022 16:30:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 557B460F60; Sun, 29 May 2022 23:30:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 844B5C385B8; Sun, 29 May 2022 23:30:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1653867030; bh=GpzTPsNqRojtOnbCgreA4wsBMUClKlvqnaoCqS7Q2yQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=KQN+Ec1m1OMjJ+UgZwlfD9T6ILbxe9+b+NogjSKzaZo1W1GjKoD9jeHRuicyTluyc Y46PdY9URSoFNW57j4/XKpmaiBgrj1ciQxaSkul9U9dTYTKiq1R56QatdIs0SAEJHx OOvlfw0dtnht5dc3r6aVTVDcQB2SvqPjf1wmm0BM= Date: Sun, 29 May 2022 16:30:29 -0700 From: Andrew Morton To: Chen Lin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Duyck , netdev@vger.kernel.org Subject: Re: [PATCH] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE Message-Id: <20220529163029.12425c1e5286d7c7e3fe3708@linux-foundation.org> In-Reply-To: <1653752373-3172-1-git-send-email-chen45464546@163.com> References: <1653752373-3172-1-git-send-email-chen45464546@163.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 28 May 2022 23:39:33 +0800 Chen Lin wrote: > netdev_alloc_frag->page_frag_alloc may cause memory corruption in > the following process: > > 1. A netdev_alloc_frag function call need alloc 200 Bytes to build a skb. > > 2. Insufficient memory to alloc PAGE_FRAG_CACHE_MAX_ORDER(32K) in > __page_frag_cache_refill to fill frag cache, then one page(eg:4K) > is allocated, now current frag cache is 4K, alloc is success, > nc->pagecnt_bias--. > > 3. Then this 200 bytes skb in step 1 is freed, page->_refcount--. > > 4. Another netdev_alloc_frag function call need alloc 5k, page->_refcount > is equal to nc->pagecnt_bias, reset page count bias and offset to > start of new frag. page_frag_alloc will return the 4K memory for a > 5K memory request. > > 5. The caller write on the extra 1k memory which is not actual allocated > will cause memory corruption. > > page_frag_alloc is for fragmented allocation. We should warn the caller > to avoid memory corruption. > Let's cc Alexander and the networking developers. > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5574,6 +5574,11 @@ void *page_frag_alloc_align(struct page_frag_cache *nc, > struct page *page; > int offset; > > + /* frag_alloc is not suitable for memory alloc which fragsz > + * is bigger than PAGE_SIZE, use kmalloc or alloc_pages instead. > + */ > + WARN_ON(fragsz > PAGE_SIZE); > + > if (unlikely(!nc->va)) { > refill: > page = __page_frag_cache_refill(nc, gfp_mask); Odd. All this does is generate a warning. If the kernel is corrupting memory, that's a bug which needs fixing?