From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D409531715C; Tue, 31 Mar 2026 17:08:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774976892; cv=none; b=mze9dHy9iTR6kXKzXvCbG08MNWdrkdqi9F0VmT/kCAaQqMc9C9w1K26yWGoQ3iXtCTYTE4QP9a51ns7S9g27+KogJaAeFF/1B21FHHkRgepYOnt8YetM+Eu0aoE5K77GG2IgExghci7Wh7qWL8TscgunLf2yJm+Zx3zBj5cEYPY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774976892; c=relaxed/simple; bh=lHd61boFM87TkJ4qEEYOfMe4upGbWpPqUxW8fstnzns=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QQQj6X8OHZtyrORjpw5wblSyGI2frVwPlZGU7Ds/r0g24+bx3Daw3EUO3kwH2z78+2UfGveSwCA32sQ1/qQ6TRkcY4VmJdfgC5sgk5rTlPy0dt1N2KSqFb8Zmjy1tpq103ouZS6WO8e9JuiBf5XF8PxKtHeGmQwXpNlHd8BpKTo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=tywmv2l7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="tywmv2l7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B7DBC2BCB1; Tue, 31 Mar 2026 17:08:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774976892; bh=lHd61boFM87TkJ4qEEYOfMe4upGbWpPqUxW8fstnzns=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tywmv2l72S2PzueDfX6eW/VAei0crrr22QxIvQTmSltITAB74c85faMpR0WVWXtWG V+8XCn26k9jUa6r1eS5MtYP5vkkWDvQRrtpX7B9UDppSXE9IRo0oV9XTdy+BG2dhua MxtQ2Fl2H3p6hi1ShHfQwnVX0JSqicJTHzQhL1OM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jiayuan Chen , Jan Kara , Jiayuan Chen , "Ritesh Harjani (IBM)" , Theodore Tso , stable@kernel.org Subject: [PATCH 6.18 267/309] ext4: fix use-after-free in update_super_work when racing with umount Date: Tue, 31 Mar 2026 18:22:50 +0200 Message-ID: <20260331161803.392136330@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331161753.468533260@linuxfoundation.org> References: <20260331161753.468533260@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen commit d15e4b0a418537aafa56b2cb80d44add83e83697 upstream. Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups reads during unmount. However, this introduced a use-after-free because update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which accesses the kobject's kernfs_node after it has been freed by kobject_del() in ext4_unregister_sysfs(): update_super_work ext4_put_super ----------------- -------------- ext4_unregister_sysfs(sb) kobject_del(&sbi->s_kobj) __kobject_del() sysfs_remove_dir() kobj->sd = NULL sysfs_put(sd) kernfs_put() // RCU free ext4_notify_error_sysfs(sbi) sysfs_notify(&sbi->s_kobj) kn = kobj->sd // stale pointer kernfs_get(kn) // UAF on freed kernfs_node ext4_journal_destroy() flush_work(&sbi->s_sb_upd_work) Instead of reordering the teardown sequence, fix this by making ext4_notify_error_sysfs() detect that sysfs has already been torn down by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call in that case. A dedicated mutex (s_error_notify_mutex) serializes ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs() to prevent TOCTOU races where the kobject could be deleted between the state_in_sysfs check and the sysfs_notify() call. Fixes: b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") Cc: Jiayuan Chen Suggested-by: Jan Kara Signed-off-by: Jiayuan Chen Reviewed-by: Ritesh Harjani (IBM) Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260319120336.157873-1-jiayuan.chen@linux.dev Signed-off-by: Theodore Ts'o Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/ext4/ext4.h | 1 + fs/ext4/super.c | 1 + fs/ext4/sysfs.c | 10 +++++++++- 3 files changed, 11 insertions(+), 1 deletion(-) --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1564,6 +1564,7 @@ struct ext4_sb_info { struct proc_dir_entry *s_proc; struct kobject s_kobj; struct completion s_kobj_unregister; + struct mutex s_error_notify_mutex; /* protects sysfs_notify vs kobject_del */ struct super_block *s_sb; struct buffer_head *s_mmp_bh; --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -5361,6 +5361,7 @@ static int __ext4_fill_super(struct fs_c timer_setup(&sbi->s_err_report, print_daily_error_info, 0); spin_lock_init(&sbi->s_error_lock); + mutex_init(&sbi->s_error_notify_mutex); INIT_WORK(&sbi->s_sb_upd_work, update_super_work); err = ext4_group_desc_init(sb, es, logical_sb_block, &first_not_zeroed); --- a/fs/ext4/sysfs.c +++ b/fs/ext4/sysfs.c @@ -555,7 +555,10 @@ static const struct kobj_type ext4_feat_ void ext4_notify_error_sysfs(struct ext4_sb_info *sbi) { - sysfs_notify(&sbi->s_kobj, NULL, "errors_count"); + mutex_lock(&sbi->s_error_notify_mutex); + if (sbi->s_kobj.state_in_sysfs) + sysfs_notify(&sbi->s_kobj, NULL, "errors_count"); + mutex_unlock(&sbi->s_error_notify_mutex); } static struct kobject *ext4_root; @@ -568,8 +571,10 @@ int ext4_register_sysfs(struct super_blo int err; init_completion(&sbi->s_kobj_unregister); + mutex_lock(&sbi->s_error_notify_mutex); err = kobject_init_and_add(&sbi->s_kobj, &ext4_sb_ktype, ext4_root, "%s", sb->s_id); + mutex_unlock(&sbi->s_error_notify_mutex); if (err) { kobject_put(&sbi->s_kobj); wait_for_completion(&sbi->s_kobj_unregister); @@ -602,7 +607,10 @@ void ext4_unregister_sysfs(struct super_ if (sbi->s_proc) remove_proc_subtree(sb->s_id, ext4_proc_root); + + mutex_lock(&sbi->s_error_notify_mutex); kobject_del(&sbi->s_kobj); + mutex_unlock(&sbi->s_error_notify_mutex); } int __init ext4_init_sysfs(void)