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 9612F3F23AE for ; Thu, 2 Apr 2026 16:37:43 +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=1775147863; cv=none; b=eJnWSAjtJLgPvpmxriG2R12FLUMUZQVJYpg4TqCgjmtyIYcemv27Ccd2qXJ1HNTozXIKPermR4JIzk50W//AF8ky2qY/qUptACZr7W8fo/kW8TpDX6NU+69YLGqr0drHPT8/3wnAztzdidV5D769Sax7B7/RJivt15AeS3fzGQg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775147863; c=relaxed/simple; bh=zDrM3WFhaUfffdL9KS0yQheID4gCwoh1TPDNejl7DLw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=N78gaq2loBaoKYlfCSwEadPkSFVJlHKJ4s6xlzAe1Euba47+7WMzkS5x+1RsotUVc+ylVfWR+2IJPSIP2jR0Kz89y9Xq3GvsUd8MLPE5xcEpgbiFdd/E0tnQzLASrmX3OfsQThQiCfeAqRwEyBYV/8fad77KXWcrbkoY0sJZ9+8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SsWhQUDO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SsWhQUDO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50847C19423; Thu, 2 Apr 2026 16:37:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775147863; bh=zDrM3WFhaUfffdL9KS0yQheID4gCwoh1TPDNejl7DLw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SsWhQUDOtonsDv2CmO39xQL2IbVa3uLHVSvPOLG1GPF0Y5jr1V3Ywskdxy5Xr5TmC d1fC5oYiQStMtbv7+Pl5HUvhBBlx3b8aE8RSCpX+pEvt0JZ3ImsJFSx9oC7EzeXvDv sorw8IlKpSosFO6wYp5rY5IUVPoMv3upeIyvkUz/dUs0ANhgKmFtKmMQSV2TYP7Odq pGjVoxXGLL2ejgxd2NB41ahxE53uEwPTpVBEVLI6GBFuLY9KXT2cwRrR99oPmfLGV0 Kq8DX6Cewx7lO5VZYttBAm83v/11jk2eSs+Y64skEGhhTCWmO51bkXDG2OITyRIcDq D6L09HBeKZsMw== From: Sasha Levin To: stable@vger.kernel.org Cc: Jiayuan Chen , Jiayuan Chen , Jan Kara , "Ritesh Harjani (IBM)" , Theodore Ts'o , stable@kernel.org, Sasha Levin Subject: [PATCH 5.15.y] ext4: fix use-after-free in update_super_work when racing with umount Date: Thu, 2 Apr 2026 12:37:40 -0400 Message-ID: <20260402163740.1407640-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026033054-vascular-atom-023e@gregkh> References: <2026033054-vascular-atom-023e@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jiayuan Chen [ Upstream commit d15e4b0a418537aafa56b2cb80d44add83e83697 ] 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 [ adapted mutex_init placement ] Signed-off-by: Sasha Levin --- fs/ext4/ext4.h | 1 + fs/ext4/super.c | 1 + fs/ext4/sysfs.c | 10 +++++++++- 3 files changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index d2158866a4b52..d99eabf846b8e 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1540,6 +1540,7 @@ 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; diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 05f1f9b7ad0c4..170bc58b61577 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4621,6 +4621,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) 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_error_work, flush_stashed_error_work); /* Register extent status tree shrinker */ diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c index aa07b78ba9104..492f5351e267b 100644 --- a/fs/ext4/sysfs.c +++ b/fs/ext4/sysfs.c @@ -513,7 +513,10 @@ static struct kobj_type ext4_feat_ktype = { 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; @@ -526,8 +529,10 @@ int ext4_register_sysfs(struct super_block *sb) 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); @@ -560,7 +565,10 @@ void ext4_unregister_sysfs(struct super_block *sb) 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) -- 2.53.0