[PATCH v2] KEYS: encrypted: Replace deprecated strcpy and improve get_derived_key

[Thorsten Blum]

Hi David,

On 14. Nov 2025, at 10:34, David Laight wrote:
> On Thu, 13 Nov 2025 22:55:45 +0100
> Thorsten Blum <thorsten.blum at linux.dev> wrote:
> 
>> strcpy() is deprecated; use the safer strscpy() and use its return
>> value, the number of bytes copied, instead of calling strlen() on the
>> destination buffer again. String truncation can be ignored since
>> 'derived_buf' is guaranteed to be large enough.
>> 
>> Link: https://github.com/KSPP/linux/issues/88
>> Signed-off-by: Thorsten Blum <thorsten.blum at linux.dev>
>> ---
>> [...]
> 
> I'm not sure this is an improvement, but has this code ever been correct?
> The buffer passed to sha256 is either:
> 	"AUTH_KEY"'\0'master_key
> or
> 	"ENC_KEY"'\0'master_key
> For short master_key the buffer is HASH_SIZE bytes and padded with zeros (ok).
> However for long master_key the length is calculated using "AUTH_KEY" so
> there is an additional trailing '\0' in the "ENC_KEY" case.

I removed the trailing '\0' in v1, but since Eric pointed out that it
changes the sha256 hash, I reverted it in v2.

Thanks,
Thorsten