linux-kernel - Re: [PATCH net-next] net: ipconfig: Replace strncpy with strscpy_pad in ic_proto

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Message-Id: <B7B14C9F-C63B-4278-AA3F-12618681482A@linux.dev>
Date: Wed, 26 Nov 2025 15:45:50 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: david laight <david.laight@...box.com>
Cc: "David S. Miller" <davem@...emloft.net>,
 David Ahern <dsahern@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: ipconfig: Replace strncpy with strscpy_pad
 in ic_proto_name

On 26. Nov 2025, at 14:50, david laight wrote:
> On Wed, 26 Nov 2025 12:13:58 +0100
> Thorsten Blum <thorsten.blum@...ux.dev> wrote:
> 
>> strncpy() is deprecated [1] for NUL-terminated destination buffers since
>> it does not guarantee NUL termination. Replace it with strscpy_pad() to
>> ensure NUL termination of the destination buffer while retaining the
>> NUL-padding behavior of strncpy().
>> 
>> Even though the identifier buffer has 252 usable bytes, strncpy()
>> intentionally copied only 251 bytes into the zero-initialized buffer,
>> implicitly relying on the last byte to act as the terminator. Switching
>> to strscpy_pad() removes the need for this trick and avoids using magic
>> numbers.
>> 
>> The source string is also NUL-terminated and satisfies the
>> __must_be_cstr() requirement of strscpy_pad().
>> 
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
>> ---
>> [...]
> 
> Wrong change...
> There is no reason to pad the destination, and the correct alternative

I agree, padding isn't necessary and strscpy() is enough.

> is to bound 'v - client_id' and then use memcpy().
> Then you don't need to modify the input buffer.

Just to confirm - this comment is about the type parsing ('client_id'
before the comma), not about copying the value after the comma, right?

Thanks,
Thorsten