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 D8818C4332F for ; Mon, 28 Mar 2022 19:48:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343892AbiC1TuT (ORCPT ); Mon, 28 Mar 2022 15:50:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344197AbiC1TsS (ORCPT ); Mon, 28 Mar 2022 15:48:18 -0400 Received: from mail-il1-f197.google.com (mail-il1-f197.google.com [209.85.166.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A43167D22 for ; Mon, 28 Mar 2022 12:44:11 -0700 (PDT) Received: by mail-il1-f197.google.com with SMTP id 5-20020a92c645000000b002c99d83806dso2842242ill.13 for ; Mon, 28 Mar 2022 12:44:11 -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=HNFnyYgATJEiRRHz7pZcGLyOeQuLL7qSe4PflAW2SKw=; b=2IdVzH3uMYsx2zdEabQSr/dyIm5QzAV7z5tCk0boTah02cOc8ddVQmBX0vSJ8du7qm 2Q/3iSOWxbn4y9gEr+oTaFtMgzMsy2a2zj9ox+djQ+A00zGgNWHi2SAILbzmsLe6Mc9f h7xNIVH94QzRAm7ko5IwrIRB21lTPJS3I1kKZDTCHG3A5EE7puZaPip2PSDZ1Wht93Os 3bYSStdhMjj7BvsaeC4cnoeynvURPnqo7jC3Z2N7MWr4oEagR/H+ljflkT2ut2a708xM L4k3gGKh+x4wWcHTSDNVsX+oI3VyHLb0W3FHteLIVLCwvXSb99AFgitIBeFTm1ZYv3xY ddNw== X-Gm-Message-State: AOAM530wr5R2+SqfVINdV+KDqlbt/x9zJXtzTAmrhxoyn+kUSBMS2doB r5OTkp/AzoNY8hDAvIUo3Y1RLhxq7NRFdhB6UKvzICFl+mnj X-Google-Smtp-Source: ABdhPJyTTIVYHX8FssxQ+YIkYMpmIDc1cjcs4jQOCuOHMvQdLXOZp0sbYL9rB6vJdic/kTMEXYjU2k+oouihwfeNmptIaETThGTK MIME-Version: 1.0 X-Received: by 2002:a05:6638:4102:b0:319:effe:d355 with SMTP id ay2-20020a056638410200b00319effed355mr13749616jab.121.1648496628060; Mon, 28 Mar 2022 12:43:48 -0700 (PDT) Date: Mon, 28 Mar 2022 12:43:48 -0700 In-Reply-To: <20220328194343.1586624-1-sashal@kernel.org> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <000000000000edd59205db4c87cd@google.com> Subject: Re: [PATCH AUTOSEL 4.14 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-ext4@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 9c07c8674b21..4d3eefff3c84 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -2147,6 +2147,15 @@ 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 > @@ -2706,6 +2715,22 @@ 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.