Re: [PATCH] proc: use strnlen() for name validation in __proc_create

[Alexey Dobriyan]

On Tue, Apr 21, 2026 at 02:26:47PM +0200, Thorsten Blum wrote:
> Replace strlen(fn) with strnlen(fn, NAME_MAX + 1) when validating the
> final path component in __proc_create().
> 
> This preserves the existing name limit while bounding the length scan to
> one byte past the maximum name length. Handle empty names separately,
> and treat names longer than NAME_MAX as too long.

256 in the code is really U8_MAX+1 (see proc_dir_entry.namelen).

The fact that NAME_MAX is also 255 is a coincidence. I didn't thought
about NAME_MAX when writing this code.

Can you just change 256 to NAME_MAX?

	/proc/alexey

> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -427,9 +427,13 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
>  	if (xlate_proc_name(name, parent, &fn) != 0)
>  		goto out;
>  	qstr.name = fn;
> -	qstr.len = strlen(fn);
> -	if (qstr.len == 0 || qstr.len >= 256) {
> -		WARN(1, "name len %u\n", qstr.len);
> +	qstr.len = strnlen(fn, NAME_MAX + 1);
> +	if (qstr.len == 0) {
> +		WARN(1, "empty name\n");
> +		return NULL;
> +	}
> +	if (qstr.len > NAME_MAX) {
> +		WARN(1, "name too long\n");