linux-kernel - Re: do_change_type(): refuse to operate on unmounted/not ours mounts

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Message-ID: <aJzi506tGJb8CzA3@tycho.pizza>
Date: Wed, 13 Aug 2025 13:09:27 -0600
From: Tycho Andersen <tycho@...ho.pizza>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Andrei Vagin <avagin@...gle.com>, Andrei Vagin <avagin@...il.com>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, criu@...ts.linux.dev,
	Linux API <linux-api@...r.kernel.org>,
	stable <stable@...r.kernel.org>
Subject: Re: do_change_type(): refuse to operate on unmounted/not ours mounts

On Wed, Aug 13, 2025 at 07:56:01PM +0100, Al Viro wrote:
> @@ -3347,18 +3360,11 @@ static int do_set_group(struct path *from_path, struct path *to_path)
>  
>  	namespace_lock();
>  
> -	err = -EINVAL;
> -	/* To and From must be mounted */
> -	if (!is_mounted(&from->mnt))
> -		goto out;
> -	if (!is_mounted(&to->mnt))
> -		goto out;
> -
> -	err = -EPERM;
> -	/* We should be allowed to modify mount namespaces of both mounts */
> -	if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
> +	err = may_change_propagation(from);
> +	if (err)
>  		goto out;
> -	if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
> +	err = may_change_propagation(from);

Just driving by, but I guess you mean "to" here.

Tycho