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 3FEAB36AB47; Tue, 31 Mar 2026 16:29:36 +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=1774974576; cv=none; b=WfV2ehpZgkMur2dLredJSxDbt2k00/IfN0aKmKx+uDTOkmK16zy3MrW2RN2GGELoYkeu1n2XmVfuHjsXdh5294tNEYaBrqKO7mRlm9eplyDYpvXhr0GpDApOmWtMJ2kOzyxpPjVAtURVoRuu8NE0qCUxphmHleMgnevSJT3rTCo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774974576; c=relaxed/simple; bh=kHwKBqjZi1xGB5fL+LrrFJsJywfmfOahe5cOM+gQkAw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RJvmlQkbn8k6siyVSnkL738mWbLpaOFWRdgJcQwFyhv8R2l2bCUL0hCLoi/K0wRozXb0Ye2FaDFlypNevfxlAJYmIoeIeTm52+WqmMZ84GFBqqU9hcd8url6IPh7Chmb2inSP1xoLkn+8nAzgbMGZ1E1Z7B+BfyQ/XJQR7wNmb0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Opk9Yp0b; 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="Opk9Yp0b" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C50D8C19423; Tue, 31 Mar 2026 16:29:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774974576; bh=kHwKBqjZi1xGB5fL+LrrFJsJywfmfOahe5cOM+gQkAw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Opk9Yp0bDTtcxnDQI6/JheuIEoK1LuV35/h8wX5pRA5PzwnvMSQzomfPmn2A9HDGh SVjjv/LHR2m+N5VkgUtcfF3ExYc9xYcxwXxkVgplbfFRVAnU9AtTNvi9eTp8ANNazm ogMeWVYpbH6v24gnCdFhtxibdgnPpXL6CqtAtygE= 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 6.6 138/175] ext4: fix use-after-free in update_super_work when racing with umount Date: Tue, 31 Mar 2026 18:22:02 +0200 Message-ID: <20260331161734.856583806@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331161729.779738837@linuxfoundation.org> References: <20260331161729.779738837@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 6.6-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 @@ -1535,6 +1535,7 @@ 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 @@ -5344,6 +5344,7 @@ 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 @@ -529,7 +529,10 @@ 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; @@ -542,8 +545,10 @@ 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); @@ -576,7 +581,10 @@ 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)