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 85A89C3A59F for ; Wed, 23 Nov 2022 09:05:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237000AbiKWJFC (ORCPT ); Wed, 23 Nov 2022 04:05:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236932AbiKWJEe (ORCPT ); Wed, 23 Nov 2022 04:04:34 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 11567102E73 for ; Wed, 23 Nov 2022 01:04:29 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B030BB81EEE for ; Wed, 23 Nov 2022 09:04:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF77EC433D6; Wed, 23 Nov 2022 09:04:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1669194266; bh=cKJsrtftiW0of52GDApWHW7SPhRuOqNhKLNmI8mWfXQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iloF+xtvbvNi0NShrW/VtSBc3ekSoqdro5oYdDoMv8A5kGJcw81l6ZaUaqP8uXctK 9t/QGYrbv6N9CxzesGLKw7J48K7zIlgNn/NM70kNGQs/L5LJizokMrusJtoFBSaHz8 kUPhO4P0e6ahtZcoFmD2FW2eP+CMEt/Qa4JFxQQQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ryusuke Konishi , syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com, Shigeru Yoshida , Andrew Morton Subject: [PATCH 4.19 029/114] nilfs2: fix use-after-free bug of ns_writer on remount Date: Wed, 23 Nov 2022 09:50:16 +0100 Message-Id: <20221123084553.010073395@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221123084551.864610302@linuxfoundation.org> References: <20221123084551.864610302@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ryusuke Konishi commit 8cccf05fe857a18ee26e20d11a8455a73ffd4efd upstream. If a nilfs2 filesystem is downgraded to read-only due to metadata corruption on disk and is remounted read/write, or if emergency read-only remount is performed, detaching a log writer and synchronizing the filesystem can be done at the same time. In these cases, use-after-free of the log writer (hereinafter nilfs->ns_writer) can happen as shown in the scenario below: Task1 Task2 -------------------------------- ------------------------------ nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_remount (R/W remount case) nilfs_attach_log_writer nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before <-- use-after-free While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This scenario diagram is based on the Shigeru Yoshida's post [1]. This patch fixes the issue by not detaching nilfs->ns_writer on remount so that this UAF race doesn't happen. Along with this change, this patch also inserts a few necessary read-only checks with superblock instance where only the ns_writer pointer was used to check if the filesystem is read-only. Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b Link: https://lkml.kernel.org/r/20221103141759.1836312-1-syoshida@redhat.com [1] Link: https://lkml.kernel.org/r/20221104142959.28296-1-konishi.ryusuke@gmail.com Signed-off-by: Ryusuke Konishi Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com Reported-by: Shigeru Yoshida Tested-by: Ryusuke Konishi Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- fs/nilfs2/segment.c | 15 ++++++++------- fs/nilfs2/super.c | 2 -- 2 files changed, 8 insertions(+), 9 deletions(-) --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -322,7 +322,7 @@ void nilfs_relax_pressure_in_lock(struct struct the_nilfs *nilfs = sb->s_fs_info; struct nilfs_sc_info *sci = nilfs->ns_writer; - if (!sci || !sci->sc_flush_request) + if (sb_rdonly(sb) || unlikely(!sci) || !sci->sc_flush_request) return; set_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags); @@ -2243,7 +2243,7 @@ int nilfs_construct_segment(struct super struct nilfs_transaction_info *ti; int err; - if (!sci) + if (sb_rdonly(sb) || unlikely(!sci)) return -EROFS; /* A call inside transactions causes a deadlock. */ @@ -2282,7 +2282,7 @@ int nilfs_construct_dsync_segment(struct struct nilfs_transaction_info ti; int err = 0; - if (!sci) + if (sb_rdonly(sb) || unlikely(!sci)) return -EROFS; nilfs_transaction_lock(sb, &ti, 0); @@ -2778,11 +2778,12 @@ int nilfs_attach_log_writer(struct super if (nilfs->ns_writer) { /* - * This happens if the filesystem was remounted - * read/write after nilfs_error degenerated it into a - * read-only mount. + * This happens if the filesystem is made read-only by + * __nilfs_error or nilfs_remount and then remounted + * read/write. In these cases, reuse the existing + * writer. */ - nilfs_detach_log_writer(sb); + return 0; } nilfs->ns_writer = nilfs_segctor_new(sb, root); --- a/fs/nilfs2/super.c +++ b/fs/nilfs2/super.c @@ -1138,8 +1138,6 @@ static int nilfs_remount(struct super_bl if ((bool)(*flags & SB_RDONLY) == sb_rdonly(sb)) goto out; if (*flags & SB_RDONLY) { - /* Shutting down log writer */ - nilfs_detach_log_writer(sb); sb->s_flags |= SB_RDONLY; /*