linux-kernel - Re: [PATCH v2] proc: Escape more characters in /proc/mounts output

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Date:   Wed, 16 Dec 2020 04:33:23 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Siddhesh Poyarekar <siddhesh@...plt.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Florian Weimer <fweimer@...hat.com>
Subject: Re: [PATCH v2] proc: Escape more characters in /proc/mounts output

On Tue, Dec 15, 2020 at 06:23:18PM +0530, Siddhesh Poyarekar wrote:

> +static char *copy_mount_devname(const void __user *data)
> +{
> +	char *p;
> +	long length;
> +
> +	if (data == NULL)
> +		return NULL;
> +
> +	length = strnlen_user(data, PATH_MAX);
> +
> +	if (!length)
> +		return ERR_PTR(-EFAULT);
> +
> +	if (length > PATH_MAX)
> +		return ERR_PTR(-EINVAL);
> +
> +	/* Ignore blank strings */
> +	if (length == 1)
> +		return NULL;
> +
> +	p = memdup_user(data, length);

Once more, with feeling: why bother?  What's wrong
with using the damn strndup_user() and then doing
whatever checks you want with the data already
copied, living in normal kernel memory, with all
string functions applicable, etc.?