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 332FAC433EF for ; Mon, 28 Mar 2022 19:50:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344115AbiC1Twe (ORCPT ); Mon, 28 Mar 2022 15:52:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344151AbiC1TsP (ORCPT ); Mon, 28 Mar 2022 15:48:15 -0400 Received: from mail-io1-f72.google.com (mail-io1-f72.google.com [209.85.166.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1F7367D18 for ; Mon, 28 Mar 2022 12:44:00 -0700 (PDT) Received: by mail-io1-f72.google.com with SMTP id w28-20020a05660205dc00b00645d3cdb0f7so11031132iox.10 for ; Mon, 28 Mar 2022 12:43:59 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:date:in-reply-to:message-id:subject :from:to:cc; bh=m2uN4NlVyz2bf6er2V8/N42952/hiadRCIADaej82As=; b=bQLkcH8LA1ghEfJYIfLWRok58zbFSnoTUlJ3L99eIZ133ick/YmsMUMrkFGgYKEYGz qB0+MCFnEBI1029pwypuuQtrMVq7ryaRfJsEG5zBiKKEILJgm78Qsej/5GMDIyo2C7Gj ZWLiFD/loJFMQwMliwHpvsSM8XpJT3S3EvPWzLU5UghAmUnq718LaKjHWWbbpuI1vqVg F1dxtkMIvWfr/kDwwpKeCvweryT6dda0uqm2ORHGn+h8MoYq/R7E1y+EarPhW+Ou9UsK whTdb2b1ZkOlrl8pkkByLzMjLJgXO7ME/o1AY43/ccvbuUIgONpFSbJIa1YDMngvCiTq apIA== X-Gm-Message-State: AOAM5321j2IAfb7icPqukE/gHQQVKuQIa9s0FtPr3dHhihkdWmtdB8HX 8q+3Nj2b6KilcgStNqW5kTA9MpvIkdV64NPK7PKF27v6X/wS X-Google-Smtp-Source: ABdhPJzWRUbxX3GwZManMLzH51Tc/vIus9FE7DMLvKBgTqTXqjMkQGlprdOtDmqTtjBJCmtze//ETM5zqaK+QVVMkeROVGYMgC7Y MIME-Version: 1.0 X-Received: by 2002:a05:6e02:1d15:b0:2c8:5edc:4362 with SMTP id i21-20020a056e021d1500b002c85edc4362mr6494255ila.308.1648496622459; Mon, 28 Mar 2022 12:43:42 -0700 (PDT) Date: Mon, 28 Mar 2022 12:43:42 -0700 In-Reply-To: <20220328194338.1586587-1-sashal@kernel.org> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <00000000000098643805db4c8734@google.com> Subject: Re: [PATCH AUTOSEL 4.19 1/2] ext4: don't BUG if someone dirty pages without asking ext4 first From: syzbot To: Sasha Levin Cc: adilger.kernel@dilger.ca, lee.jones@linaro.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, sashal@kernel.org, stable@vger.kernel.org, tytso@mit.edu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Theodore Ts'o > > [ Upstream commit cc5095747edfb054ca2068d01af20be3fcc3634f ] > > [un]pin_user_pages_remote is dirtying pages without properly warning > the file system in advance. A related race was noted by Jan Kara in > 2018[1]; however, more recently instead of it being a very hard-to-hit > race, it could be reliably triggered by process_vm_writev(2) which was > discovered by Syzbot[2]. > > This is technically a bug in mm/gup.c, but arguably ext4 is fragile in > that if some other kernel subsystem dirty pages without properly > notifying the file system using page_mkwrite(), ext4 will BUG, while > other file systems will not BUG (although data will still be lost). > > So instead of crashing with a BUG, issue a warning (since there may be > potential data loss) and just mark the page as clean to avoid > unprivileged denial of service attacks until the problem can be > properly fixed. More discussion and background can be found in the > thread starting at [2]. > > [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz > [2] https://lore.kernel.org/r/Yg0m6IjcNmfaSokM@google.com > > Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com > Reported-by: Lee Jones > Signed-off-by: Theodore Ts'o > Link: https://lore.kernel.org/r/YiDS9wVfq4mM2jGK@mit.edu > Signed-off-by: Sasha Levin > --- > fs/ext4/inode.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 7959aae4857e..96cf0f57ca95 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -2148,6 +2148,15 @@ static int ext4_writepage(struct page *page, > else > len = PAGE_SIZE; > > + /* Should never happen but for bugs in other kernel subsystems */ > + if (!page_has_buffers(page)) { > + ext4_warning_inode(inode, > + "page %lu does not have buffers attached", page->index); > + ClearPageDirty(page); > + unlock_page(page); > + return 0; > + } > + > page_bufs = page_buffers(page); > /* > * We cannot do block allocation or other extent handling in this > @@ -2697,6 +2706,22 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) > wait_on_page_writeback(page); > BUG_ON(PageWriteback(page)); > > + /* > + * Should never happen but for buggy code in > + * other subsystems that call > + * set_page_dirty() without properly warning > + * the file system first. See [1] for more > + * information. > + * > + * [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz > + */ > + if (!page_has_buffers(page)) { > + ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", page->index); > + ClearPageDirty(page); > + unlock_page(page); > + continue; > + } > + > if (mpd->map.m_len == 0) > mpd->first_page = page->index; > mpd->next_page = page->index + 1; > -- > 2.34.1 > I see the command but can't find the corresponding bug. The email is sent to syzbot+HASH@syzkaller.appspotmail.com address but the HASH does not correspond to any known bug. Please double check the address.