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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 AF86AC432BE for ; Wed, 1 Sep 2021 15:42:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94A6160F3A for ; Wed, 1 Sep 2021 15:42:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343779AbhIAPnl (ORCPT ); Wed, 1 Sep 2021 11:43:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343705AbhIAPnh (ORCPT ); Wed, 1 Sep 2021 11:43:37 -0400 Received: from mail-yb1-xb2a.google.com (mail-yb1-xb2a.google.com [IPv6:2607:f8b0:4864:20::b2a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1E291C061760 for ; Wed, 1 Sep 2021 08:42:41 -0700 (PDT) Received: by mail-yb1-xb2a.google.com with SMTP id q70so5892619ybg.11 for ; Wed, 01 Sep 2021 08:42:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8aCBEJKtdvAJtrTrGgodt4LUm0+Z7gqZfpmD/VmzxRk=; b=R1ryQlLrLKGt/v8//Q9rGKUHdcgBDrp6/sYQ33GTCTpJ5Un4Skro0oOst3pFa2vmzj 0eRJUNhpZce5+8lwfZ3e5akFkVTbhP2ghPnNi3hUABx/JlqLQyuA6pychIwvcmbqln/i CR26ejZI3VeSRhRM2ycMIXajd+c3VGOQ2S/iLnA4ZhA/O55klYq5+MCnjcsfecphzRSV K+FMeY8OE+XpUXLB0I9AXogd+d0Qsn72gxpzdG4UJzafkOgNmMXj8X19Dr+JH9GElsrS 5pfGbfXWHsUfRVe70ybV7MTIxJza2dg/DX/SJDyL+6atpZIIKQxhh4+KI9jfDbMYpqSP CcdA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=8aCBEJKtdvAJtrTrGgodt4LUm0+Z7gqZfpmD/VmzxRk=; b=FWPg+3kVuWZvb5AdMrtrpvF46Xg9U9LGKHMxi+JXg11ad1Y8qGQiFGo0NdUAVMdCvZ RwxYuHk1ibObGdurOqsaeSOzhwfoynmjEdEp39R+JqI/78H3aNDAztAqqI2jEFCwNT7g 9wUWp1k9tJLNyrjkyckJX5qj0q4L4E0h9NiE+q/3/ocl2Rp4MNKTd2h0wVlx6QX8gr6A O1gF632+bFqMP8vYW9jXFJonQs6c3FKBD7SsBI2whPUECxpQ9x8ONabn54wl2++8B5Xu y7dG3Xw17Vh9Gr2vXBJQw9lLbd/kJBl5ffE0dPquMXOxJ5CPHCjHA0mAp2rCJIgQpk0/ kS7w== X-Gm-Message-State: AOAM533s5pbNLX1oPxO/XzaJQs1suBh/dFNlc443x+rChxQqOj5VrZOp uXTifpjvJQcEEgxQGdKTL1OEw73OFetg0YjAjv20Hg== X-Google-Smtp-Source: ABdhPJwgQPH0nvbXpOtJyJ8qfGoULlT527Pv1mAagLgarkJHCp5SC7DsgZ+zIsArG/MC/YiqIV0K+Xpv+P7vOkdmGkQ= X-Received: by 2002:a25:9ac6:: with SMTP id t6mr189907ybo.190.1630510960178; Wed, 01 Sep 2021 08:42:40 -0700 (PDT) MIME-Version: 1.0 References: <20210827191858.2037087-1-surenb@google.com> <20210827191858.2037087-3-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 1 Sep 2021 08:42:29 -0700 Message-ID: Subject: Re: [PATCH v8 2/3] mm: add a field to store names for private anonymous memory To: Michal Hocko Cc: Andrew Morton , Colin Cross , Sumit Semwal , Dave Hansen , Kees Cook , Matthew Wilcox , "Kirill A . Shutemov" , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Al Viro , Randy Dunlap , Kalesh Singh , Peter Xu , rppt@kernel.org, Peter Zijlstra , Catalin Marinas , vincenzo.frascino@arm.com, =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , Axel Rasmussen , Andrea Arcangeli , Jann Horn , apopple@nvidia.com, John Hubbard , Yu Zhao , Will Deacon , fenghua.yu@intel.com, thunder.leizhen@huawei.com, Hugh Dickins , feng.tang@intel.com, Jason Gunthorpe , Roman Gushchin , Thomas Gleixner , krisman@collabora.com, chris.hyser@oracle.com, Peter Collingbourne , "Eric W. Biederman" , Jens Axboe , legion@kernel.org, Rolf Eike Beer , Muchun Song , Viresh Kumar , Thomas Cedeno , sashal@kernel.org, cxfcosmos@gmail.com, Rasmus Villemoes , LKML , linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 1, 2021 at 1:10 AM 'Michal Hocko' via kernel-team wrote: > > On Fri 27-08-21 12:18:57, Suren Baghdasaryan wrote: > [...] > > +static void replace_vma_anon_name(struct vm_area_struct *vma, const char *name) > > +{ > > + if (!name) { > > + free_vma_anon_name(vma); > > + return; > > + } > > + > > + if (vma->anon_name) { > > + /* Should never happen, to dup use dup_vma_anon_name() */ > > + WARN_ON(vma->anon_name == name); > > What is the point of this warning? I wanted to make sure replace_vma_anon_name() is not used from inside vm_area_dup() or some similar place (does not exist today but maybe in the future) where "new" vma is a copy of "orig" vma and new->anon_name==orig->anon_name. If someone by mistake calls replace_vma_anon_name(new, orig->anon_name) and new->anon_name==orig->anon_name then they will keep pointing to the same name pointer, which breaks an assumption that ->anon_name pointers are not shared among vmas even if the string is the same. That would eventually lead to use-after-free error. After the next patch implementing refcounting, the similar situation would lead to both new and orig vma pointing to the same anon_vma_name structure without raising the refcount, which would also lead to use-after-free error. That's why the above comment asks to use dup_vma_anon_name() if this warning ever happens. I can remove the warning but I thought the problem is subtle enough to put some safeguards. > > > + > > + /* Same name, nothing to do here */ > > + if (!strcmp(name, vma->anon_name)) > > + return; > > + > > + free_vma_anon_name(vma); > > + } > > + vma->anon_name = kstrdup(name, GFP_KERNEL); > > +} > -- > Michal Hocko > SUSE Labs > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >