Subject: Re: [PATCH net-next] net: ipconfig: replace strncpy with strscpy

From: Jakub Kicinski <[email-masked]>
Date: Tue, 15 Apr 2025 17:19:27 -0700

On Tue, 15 Apr 2025 17:35:36 +0100 Simon Horman wrote:
> > @@ -1690,7 +1690,7 @@ static int __init ic_proto_name(char *name)
> >  			*v = 0;
> >  			if (kstrtou8(client_id, 0, dhcp_client_identifier))
> >  				pr_debug("DHCP: Invalid client identifier type\n");
> > -			strncpy(dhcp_client_identifier + 1, v + 1, 251);
> > +			strscpy(dhcp_client_identifier + 1, v + 1, 251);  
> 
> As an aside, I'm curious to know why the length is 251
> rather than 252 (sizeof(dhcp_client_identifier) -1).
> But that isn't strictly related to this patch.

Isn't this because strncpy() doesn't nul-terminate, and since this is a
static variable if we use len - 1 we guarantee that there will be a null
byte at the end? If we switch to strscpy we'll make the max string len
1 char shorter.