linux-kernel - Re: [PATCH 2/2] acct: block access to kernel internal filesystems

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Message-ID: <20250211205418.GI1977892@ZenIV>
Date: Tue, 11 Feb 2025 20:54:18 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Christian Brauner <brauner@...nel.org>
Cc: Zicheng Qu <quzicheng@...wei.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>, jlayton@...nel.org,
	axboe@...nel.dk, joel.granados@...nel.org, tglx@...utronix.de,
	hch@....de, len.brown@...el.com, pavel@....cz, pengfei.xu@...el.com,
	rafael@...nel.org, tanghui20@...wei.com, zhangqiao22@...wei.com,
	judy.chenhui@...wei.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
	linux-pm@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] acct: block access to kernel internal filesystems

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...