Re: [PATCH v6 16/17] lib/bootconfig: fix sign-compare in xbc_node_compose_key_after()

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 17 Mar 2026 16:55:49 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> > --- a/lib/bootconfig.c
> > +++ b/lib/bootconfig.c
> > @@ -319,10 +319,10 @@ int __init xbc_node_compose_key_after(struct xbc_node *root,
> >  			       depth ? "." : "");
> >  		if (ret < 0)
> >  			return ret;
> > -		if (ret >= size) {
> > +		if (ret >= (int)size) {  
> 
> nit:
> 
> 	if ((size_t)ret >= size) {
> 
> because sizeof(size_t) > sizeof(int).

I don't think we need to worry about this. But this does bring up an issue.
ret comes from:

		ret = snprintf(buf, size, "%s%s", xbc_node_get_data(node),
			       depth ? "." : "");

Where size is of type size_t

snprintf() takes size_t but returns int.

snprintf() calls vsnprintf() which has:

	size_t len, pos;

Where pos is incremented based on fmt, and vsnprintf() returns:

	return pos;

Which can overflow.

Now, honestly, we should never have a 2Gig string as that would likely
cause other horrible things. Does size really need to be size_t?

Perhaps we should have:

	if (WARN_ON_ONCE(size > MAX_INT))
		return -EINVAL;

?

-- Steve