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 7B176C433F5 for ; Thu, 10 Feb 2022 19:35:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344034AbiBJTfp (ORCPT ); Thu, 10 Feb 2022 14:35:45 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:44506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242374AbiBJTfo (ORCPT ); Thu, 10 Feb 2022 14:35:44 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F859E61 for ; Thu, 10 Feb 2022 11:35:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=sm+e1eXnxMV9mmXhJaaWMCKB3nawohVI61dfIEdJPQ4=; b=wYcsSEvm9pVoVb47G8HPuCHrqn f8ezR3VKR3Dl+FM87qHJ66CPVSg0HUX4TmblczryfOeTFipVoBhNqjlw7Jk2xSOSu3OICmz6jTiCr aaV/St6BfrBDbdyhM/8PyDj+Y3Dy3/lNE/t6go6UmR1LWQVM1ArXbpFIdKW9RndHV9xn7vYwdBEMF sZK8wVXGvMSi8Wd39tLHKGrRwm+XkWy2uL5R0Ib92NEgEay/nRpr7k9zXPFsBNaoB/2q3lsPHs5AZ 6iuGMsIN4Tl09RduDCj+rvhzxvm/O2uvRMdgqaNTlQAlljtVctrLdxPTMduNgixNdMMcq10IurUsi v+4nbjHg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nIFDY-009hbc-RP; Thu, 10 Feb 2022 19:35:00 +0000 Date: Thu, 10 Feb 2022 19:35:00 +0000 From: Matthew Wilcox To: Suren Baghdasaryan Cc: Michal Hocko , Andrew Morton , Colin Cross , Sumit Semwal , Dave Hansen , Kees Cook , "Kirill A . Shutemov" , Vlastimil Babka , Johannes Weiner , "Eric W. Biederman" , brauner@kernel.org, legion@kernel.org, ran.xiaokai@zte.com.cn, sashal@kernel.org, Chris Hyser , Davidlohr Bueso , Peter Collingbourne , caoxiaofeng@yulong.com, David Hildenbrand , Cyrill Gorcunov , linux-mm , LKML , kernel-team , syzbot+aa7b3d4b35f9dc46a366@syzkaller.appspotmail.com Subject: Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used after vma is freed Message-ID: References: <20220210043215.42794-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 10, 2022 at 08:00:15AM -0800, Suren Baghdasaryan wrote: > On Thu, Feb 10, 2022 at 7:27 AM Matthew Wilcox wrote: > > > > On Thu, Feb 10, 2022 at 07:18:24AM -0800, Suren Baghdasaryan wrote: > > > On Thu, Feb 10, 2022 at 4:40 AM 'Michal Hocko' via kernel-team > > > wrote: > > > > > > > > On Wed 09-02-22 20:32:15, Suren Baghdasaryan wrote: > > > > > When adjacent vmas are being merged it can result in the vma that was > > > > > originally passed to madvise_update_vma being destroyed. In the current > > > > > implementation, the name parameter passed to madvise_update_vma points > > > > > directly to vma->anon_name->name and it is used after the call to > > > > > vma_merge. In the cases when vma_merge merges the original vma and > > > > > destroys it, this will result in use-after-free bug as shown below: > > > > > > > > > > madvise_vma_behavior << passes vma->anon_name->name as name param > > > > > madvise_update_vma(name) > > > > > vma_merge > > > > > __vma_adjust > > > > > vm_area_free <-- frees the vma > > > > > replace_vma_anon_name(name) <-- UAF > > > > > > > > > > Fix this by raising the name refcount and stabilizing it. Introduce > > > > > vma_anon_name_{get/put} API for this purpose. > > > > > > > > What is the reason that madvise_update_vma uses the naked name rather > > > > than the encapsulated anon_vma_name? This really just begs for problems. > > > > > > The reason for that is the second place it's being used from the prctl syscall: > > > > > > prctl_set_vma > > > madvise_set_anon_name > > > madvise_vma_anon_name > > > madvise_update_vma > > > > > > In that case the name parameter is not part of any anon_vma_name > > > struct and therefore is stable. I can add a comment to > > > madvise_update_vma indicating that the name parameter has to be stable > > > if that helps. > > > > Seems to me it'd simplify things if replace_vma_anon_name() and > > madvise_vma_anon_name() took a struct anon_vma_name instead of > > a bare char *. You could construct it in madvise_set_anon_name(). > > Ok, this can be done. However I don't think changing > replace_vma_anon_name() to accept a struct anon_vma_name would be a > good idea. Reader might think that the object being passed will become > the vma->anon_name of the vma, while in reality that's not the case. Why woud we not want that to be the case? It's a refcounted name. I don't see why it shouldn't be shared between multiple VMAs that have the same name?