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=-12.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2BBB1C433F5 for ; Wed, 22 Sep 2021 14:31:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F586611C9 for ; Wed, 22 Sep 2021 14:31:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236249AbhIVOc3 (ORCPT ); Wed, 22 Sep 2021 10:32:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32196 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232401AbhIVOc2 (ORCPT ); Wed, 22 Sep 2021 10:32:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632321058; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=H9MFwjIYK3NzURsIL5ZeXXjauXt11emCz529o4qozFY=; b=RDXhkccJok5H6fMPJGPvKH+D6VD23YKtFt/ITvNl23chYDBPmro6xOAki/ASCUvIiJpedt p4sYdNyUVSCZtoVc6qc5Qtx9BYL26hjJiVPyIzxeF581VD0HbTZcYXqM7mYPoXSAvUNoZV 6+TE/dPBTNIl92KYWgr9eh+ZDHsAOzc= Received: from mail-qv1-f69.google.com (mail-qv1-f69.google.com [209.85.219.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-228-KnOO83a4OgWab3KjQLmzFw-1; Wed, 22 Sep 2021 10:30:56 -0400 X-MC-Unique: KnOO83a4OgWab3KjQLmzFw-1 Received: by mail-qv1-f69.google.com with SMTP id ci14-20020a056214054e00b0037a75ff56f9so11439601qvb.23 for ; Wed, 22 Sep 2021 07:30:56 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=H9MFwjIYK3NzURsIL5ZeXXjauXt11emCz529o4qozFY=; b=rBUGfZtc1whzMS67huVuH2U3q6LLhbu0FEZAwiWVLqO4MFeEEIRZkPusjonBIw9eWj I6LAMSRH9KBGa6mT4urLpXUSDfz+9VNS/lNZPLV8FmlBmtWKb/OgsaBKKvrZkZQqcS2A OvzX976p2i+ZhXBM+y4eoQxKfYZzBtWfoSPDDtnezC5+E8z5BUZfSBc46yBx0xlwgNPK gqLM4bHwUMJCu6gA+btZmTtRBOarS9Dtv5gBjlFtiQY94zdweMKaEsV0uHvwLg5uknEa jMWVjbDOurZMovRQRBWcNtTrrRBItqUdHZk3v+r8SgpbNubAE+AnmI2QiUrVFlSHaV/e zcCg== X-Gm-Message-State: AOAM530Sxqv8d0OD0pEBf5blJ4q94XO7gwXyedfzgpMXpSdOxoGNix/+ CKoEWm51m4kcmJMOXavUFUgFLFL8DiJgCxqKmnIPTpyFPejUeP1dFJZRJqIwI+jpX/6CtgXNRqj bIcqjOYQAS9s3kyPcI15bQh3jPw== X-Received: by 2002:ac8:1c6:: with SMTP id b6mr32958211qtg.221.1632321056090; Wed, 22 Sep 2021 07:30:56 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyQAVBr6hBwwFSYKO7U1/khHUr5y9tSTMCIoPdoZ894eUZ+OrVYZ3xfOPFjOhJbFSSfttPIFg== X-Received: by 2002:ac8:1c6:: with SMTP id b6mr32958174qtg.221.1632321055765; Wed, 22 Sep 2021 07:30:55 -0700 (PDT) Received: from t490s ([2607:fea8:56a2:9100::d3ec]) by smtp.gmail.com with ESMTPSA id f83sm1917615qke.79.2021.09.22.07.30.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Sep 2021 07:30:55 -0700 (PDT) Date: Wed, 22 Sep 2021 10:30:53 -0400 From: Peter Xu To: Nadav Amit Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Nadav Amit , Andrea Arcangeli , stable@vger.kernel.org Subject: Re: [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap() Message-ID: References: <20210921200247.25749-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210921200247.25749-1-namit@vmware.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Sep 21, 2021 at 01:02:47PM -0700, Nadav Amit wrote: > From: Nadav Amit > > A race is possible when a process exits, its VMAs are removed > by exit_mmap() and at the same time userfaultfd_writeprotect() is > called. > > The race was detected by KASAN on a development kernel, but it appears > to be possible on vanilla kernels as well. > > Use mmget_not_zero() to prevent the race as done in other userfaultfd > operations. > > Cc: Peter Xu > Cc: Andrea Arcangeli > Cc: stable@vger.kernel.org > Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") > Signed-off-by: Nadav Amit Reviewed-by: Peter Xu Thanks! -- Peter Xu