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

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Message-ID: <16bc3288-ede5-4777-aac4-60426aef1321@amd.com>
Date: Thu, 10 Apr 2025 13:40:42 -0700
From: "Nelson, Shannon" <shannon.nelson@....com>
To: Pranav Tyagi <pranav.tyagi03@...il.com>
Cc: davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
 skhan@...uxfoundation.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH] net: ipconfig: replace strncpy with strscpy_pad

On 4/10/2025 12:59 PM, Pranav Tyagi wrote:
> 
> On Wed, Apr 9, 2025 at 3:14 AM Nelson, Shannon <shannon.nelson@....com> wrote:
>>
>> On 4/8/2025 11:57 AM, Pranav Tyagi wrote:
>>>
>>> Replace the deprecated strncpy() function with strscpy_pad() as the
>>> destination buffer is NUL-terminated and requires
>>> trailing NUL-padding
>>>
>>> Signed-off-by: Pranav Tyagi <pranav.tyagi03@...il.com>
>>
>> There should be a Fixes tag here, and usually we put the 'net' tree
>> indicator inside the tag, like this: [PATCH net]
>>
>>
>>> ---
>>>    net/ipv4/ipconfig.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
>>> index c56b6fe6f0d7..7c238d19328f 100644
>>> --- a/net/ipv4/ipconfig.c
>>> +++ b/net/ipv4/ipconfig.c
>>> @@ -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_pad(dhcp_client_identifier + 1, v + 1, 251);
>>
>> The strncpy() action, as well as the memcpy() into
>> dhcp_client_identifier elsewhere, are not padding to the end, so I think
>> this only needs to be null-terminated, not fully padded.  If full
>> padding is needed, please let us know why.
>>
>> sln
>>
>>>                           *v = ',';
>>>                   }
>>>                   return 1;
>>> --
>>> 2.49.0
>>>
>>>
>>
> 
> My initial assumption was on the fact that dhcp_client_identifier
> is directly used in DHCP packet construction
> and may be parsed byte-wise. But on going through the code again
> I see that it does not require to be fully padded.
> Would strscpy() suffice? as it ensures null-termination and
> does not fully pad the buffer.

Yes, strscpy() should work.
sln


> 
> Regards
> Pranav Tyagi