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	Tue, 11 Feb 2025 20:54:18 +0000
Date: Tue, 11 Feb 2025 20:54:18 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Christian Brauner <brauner@kernel.org>
Cc: Zicheng Qu <quzicheng@huawei.com>,
	Linus Torvalds <torvalds@linux-foundation.org>, jlayton@kernel.org,
	axboe@kernel.dk, joel.granados@kernel.org, tglx@linutronix.de,
	hch@lst.de, len.brown@intel.com, pavel@ucw.cz, pengfei.xu@intel.com,
	rafael@kernel.org, tanghui20@huawei.com, zhangqiao22@huawei.com,
	judy.chenhui@huawei.com, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	linux-pm@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 2/2] acct: block access to kernel internal filesystems
Message-ID: <20250211205418.GI1977892@ZenIV>
References: <20250211-work-acct-v1-0-1c16aecab8b3@kernel.org>
 <20250211-work-acct-v1-2-1c16aecab8b3@kernel.org>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Tue, Feb 11, 2025 at 06:16:00PM +0100, Christian Brauner wrote:
> There's no point in allowing anything kernel internal nor procfs or
> sysfs.

> +	/* Exclude kernel kernel internal filesystems. */
> +	if (file_inode(file)->i_sb->s_flags & (SB_NOUSER | SB_KERNMOUNT)) {
> +		kfree(acct);
> +		filp_close(file, NULL);
> +		return -EINVAL;
> +	}
> +
> +	/* Exclude procfs and sysfs. */
> +	if (file_inode(file)->i_sb->s_iflags & SB_I_USERNS_VISIBLE) {
> +		kfree(acct);
> +		filp_close(file, NULL);
> +		return -EINVAL;
> +	}

That looks like a really weird way to test it, especially the second
part...