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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21B36C433FF for ; Wed, 31 Jul 2019 15:33:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E6748206A3 for ; Wed, 31 Jul 2019 15:33:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726185AbfGaPdr (ORCPT ); Wed, 31 Jul 2019 11:33:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:44946 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725209AbfGaPdr (ORCPT ); Wed, 31 Jul 2019 11:33:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 39D45AC68; Wed, 31 Jul 2019 15:14:17 +0000 (UTC) Subject: Re: [PATCH 4.9 57/83] mm: prevent get_user_pages() from overflowing page refcount To: Greg Kroah-Hartman , linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org, Jann Horn , Matthew Wilcox , Linus Torvalds , Ben Hutchings References: <20190609164127.843327870@linuxfoundation.org> <20190609164132.774263938@linuxfoundation.org> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy 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5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: <6650323f-dbc9-f069-000b-f6b0f941a065@suse.cz> Date: Wed, 31 Jul 2019 17:14:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190609164132.774263938@linuxfoundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 6/9/19 6:42 PM, Greg Kroah-Hartman wrote: > From: Linus Torvalds > > commit 8fde12ca79aff9b5ba951fce1a2641901b8d8e64 upstream. > > If the page refcount wraps around past zero, it will be freed while > there are still four billion references to it. One of the possible > avenues for an attacker to try to make this happen is by doing direct IO > on a page multiple times. This patch makes get_user_pages() refuse to > take a new page reference if there are already more than two billion > references to the page. > > Reported-by: Jann Horn > Acked-by: Matthew Wilcox > Signed-off-by: Linus Torvalds > [bwh: Backported to 4.9: > - Add the "err" variable in follow_hugetlb_page() > - Adjust context] > Signed-off-by: Ben Hutchings > Signed-off-by: Greg Kroah-Hartman > --- > mm/gup.c | 45 ++++++++++++++++++++++++++++++++++----------- > mm/hugetlb.c | 16 +++++++++++++++- > 2 files changed, 49 insertions(+), 12 deletions(-) > ... > @@ -1231,6 +1240,20 @@ struct page *get_dump_page(unsigned long > */ > #ifdef CONFIG_HAVE_GENERIC_RCU_GUP > > +/* > + * Return the compund head page with ref appropriately incremented, > + * or NULL if that failed. > + */ > +static inline struct page *try_get_compound_head(struct page *page, int refs) > +{ > + struct page *head = compound_head(page); > + if (WARN_ON_ONCE(page_ref_count(head) < 0)) > + return NULL; > + if (unlikely(!page_cache_add_speculative(head, refs))) > + return NULL; > + return head; > +} > + > #ifdef __HAVE_ARCH_PTE_SPECIAL > static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > int write, struct page **pages, int *nr) > @@ -1263,9 +1286,9 @@ static int gup_pte_range(pmd_t pmd, unsi > > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > - head = compound_head(page); > > - if (!page_cache_get_speculative(head)) > + head = try_get_compound_head(page, 1); BTW, several arches in 4.9, including x86, have arch-specific fast gup implementation, which is not touched by this backport. Didn't check if Jann's exploit ends up using the fast on non-fast one, though.