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

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Message-ID: <20250415171927.5108d252@kernel.org>
Date: Tue, 15 Apr 2025 17:19:27 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Simon Horman <horms@...nel.org>
Cc: Pranav Tyagi <pranav.tyagi03@...il.com>, davem@...emloft.net,
 dsahern@...nel.org, edumazet@...gle.com, pabeni@...hat.com,
 skhan@...uxfoundation.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH net-next] net: ipconfig: replace strncpy with strscpy

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.