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 0C7CBC433EF for ; Mon, 28 Mar 2022 19:49:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344089AbiC1TvC (ORCPT ); Mon, 28 Mar 2022 15:51:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49664 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343990AbiC1TsD (ORCPT ); Mon, 28 Mar 2022 15:48:03 -0400 Received: from mail-io1-f70.google.com (mail-io1-f70.google.com [209.85.166.70]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 338FE69727 for ; Mon, 28 Mar 2022 12:43:42 -0700 (PDT) Received: by mail-io1-f70.google.com with SMTP id g16-20020a05660226d000b00638d8e1828bso11028885ioo.13 for ; Mon, 28 Mar 2022 12:43:42 -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=NJDz21iPC6Oy7Z25WXrtZdMywwSD6fY8fdtK24gSKs8=; b=kumeP/5vWiK/wsL9ku3NmpgpW532UKdaEXTf+Zxur7zS/oNwihXO5+k3Q0K5naYv42 Fu/y+KEXfde7qwXFZoiu65KOpGBHjFD+MuXC885ClPqDnQELgYF/LxicyZ7WZyA4b2xR 1IulbXC8cdqehcgtc0U4FKbOvf88M2WEU4Wv326R9HULE4arxnfXnrp6nZcmh0z1CP4u z+kn4V75l1UuHg+mxtTVBdwA2lVQXtlzl3tnrpki+Gx2tC9bF2TX3odzwZVzhl+29jdx WjE26XZ0YzI/uOI9+xQ97e6HAX2dNwz36lp3o2xvhjpAW/lfLX2Z62gF0OyW/twZ7Fmy KwaA== X-Gm-Message-State: AOAM531x3LKsi3fSCbPU3fsUO/6guI3kjqHKlhAQg46Se5C/7WagITr4 M2NhdPcW5J5JPOz/7HtlwJEe0063Ll6DRQlU+Upe4penpyMm X-Google-Smtp-Source: ABdhPJzvSQ38RG+7i/uzpKR13dDxbyddRvhA6/nZYHkhO4MPhe0pFAAtAkV3G/d96FgcYOW74mC2StkZfmG+s/uTy6qljc6qF4qQ MIME-Version: 1.0 X-Received: by 2002:a05:6602:26ce:b0:649:5967:ca14 with SMTP id g14-20020a05660226ce00b006495967ca14mr7146001ioo.97.1648496609726; Mon, 28 Mar 2022 12:43:29 -0700 (PDT) Date: Mon, 28 Mar 2022 12:43:29 -0700 In-Reply-To: <20220328194322.1586401-4-sashal@kernel.org> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <000000000000d61a3d05db4c86ac@google.com> Subject: Re: [PATCH AUTOSEL 5.10 4/8] 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 d59474a54189..96546df39bcf 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -2023,6 +2023,15 @@ 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 > @@ -2626,6 +2635,22 @@ 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.