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 C3F3BC47082 for ; Thu, 14 Apr 2022 13:58:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345822AbiDNNyV (ORCPT ); Thu, 14 Apr 2022 09:54:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243479AbiDNNp4 (ORCPT ); Thu, 14 Apr 2022 09:45:56 -0400 Received: from mail-il1-f198.google.com (mail-il1-f198.google.com [209.85.166.198]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E7C605FE4 for ; Thu, 14 Apr 2022 06:43:31 -0700 (PDT) Received: by mail-il1-f198.google.com with SMTP id v11-20020a056e0213cb00b002cbcd972206so3023480ilj.11 for ; Thu, 14 Apr 2022 06:43:31 -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=2VrWD7opmJFlL7T6rbv4Z/qjhpNRkx9YT608QCgTBxY=; b=3V8LG2XYr0LwINolPdNLlYveEdBw3V4RKhi06uKvqQdlPzas3x6B/Ob+ehYtBIzCGH BEl0jNfvnSPoE4LGVDC69CN+VS4u4RGEMu1DkHv9Zk3wLh0qEew3Hx6OKtOUoUPehDz3 eWOfxWT9nqhmexAyqw01uIWj7exxg/LnpatSclBulwFZNFhWQ8dJZuM9BnJ0NAA3xx4x nzItMWkBIUvxnlWm+VjteDa8VsP5F1bk3FEZFO74Vh1Sjjlq1Wnqyo/PDQ5+1Ch6cUa4 ErbHNKQOUWSygeQxN1UW5aqy+OscbrKhmJoAC3U4uMhwSe+muKwMdNt2PuBQzEpTH85X WKtw== X-Gm-Message-State: AOAM5329sZ5oN2X9CuggNOp/7ZUaATDSYGt1tv2NwVaKop6Bhz4Co5RF thpF8Kle5iOS60YZ1h9IVfezB3sXVQ2//wqpaafGPnRhue65 X-Google-Smtp-Source: ABdhPJzJ0j2GI6IjPYE4GhvLOvIIkMP1+B/Dag4tF8n6BC5RtTyEfK6x/ex5ztjKQ7agboIv4tJcdcFCyqpld4pc3aAI1H4tRzqy MIME-Version: 1.0 X-Received: by 2002:a05:6602:14cb:b0:646:3b7d:6aee with SMTP id b11-20020a05660214cb00b006463b7d6aeemr1254503iow.178.1649943811352; Thu, 14 Apr 2022 06:43:31 -0700 (PDT) Date: Thu, 14 Apr 2022 06:43:31 -0700 In-Reply-To: <20220414110903.185132971@linuxfoundation.org> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <000000000000c6715b05dc9d7ab5@google.com> Subject: Re: [PATCH 5.4 289/475] ext4: dont BUG if someone dirty pages without asking ext4 first From: syzbot To: Greg Kroah-Hartman Cc: gregkh@linuxfoundation.org, lee.jones@linaro.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: stable@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 dcbd8ac8d471..0d62f05f8925 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -2161,6 +2161,15 @@ 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 > @@ -2710,6 +2719,22 @@ 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.