Re: [PATCH v2] scsi: ibmvscsi_tgt: replace deprecated strncpy with strscpy

[Tyrel Datwyler <turtle.in.the.kernel@gmail.com>]

On 12/12/23 13:23, Kees Cook wrote:
> On Tue, Dec 12, 2023 at 01:20:20AM +0000, Justin Stitt wrote:
>> strncpy() is deprecated for use on NUL-terminated destination strings
>> [1] and as such we should prefer more robust and less ambiguous string
>> interfaces.
>>
>> We don't need the NUL-padding behavior that strncpy() provides as vscsi
>> is NUL-allocated in ibmvscsis_probe() which proceeds to call
>> ibmvscsis_adapter_info():
>> |       vscsi = kzalloc(sizeof(*vscsi), GFP_KERNEL);
>>
>> ibmvscsis_probe() -> ibmvscsis_handle_crq() -> ibmvscsis_parse_command()
>> -> ibmvscsis_mad() -> ibmvscsis_process_mad() -> ibmvscsis_adapter_info()
>>
>> Following the same idea, `partition_name` is defiend as:
>> |       static char partition_name[PARTITION_NAMELEN] = "UNKNOWN";
>> ... which is NUL-padded already, meaning strscpy() is the best option.
>>
>> Considering the above, a suitable replacement is `strscpy` [2] due to
>> the fact that it guarantees NUL-termination on the destination buffer
>> without unnecessarily NUL-padding.
>>
>> However, for cap->name and info let's use strscpy_pad as they are
>> allocated via dma_alloc_coherent():
>> |       cap = dma_alloc_coherent(&vscsi->dma_dev->dev, olen, &token,
>> |                                GFP_ATOMIC);
>> &
>> |       info = dma_alloc_coherent(&vscsi->dma_dev->dev, sizeof(*info), &token,
>> |                                 GFP_ATOMIC);
>>
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
>> Link: https://github.com/KSPP/linux/issues/90
>> Cc: linux-hardening@vger.kernel.org
>> Signed-off-by: Justin Stitt <justinstitt@google.com>
> 
> This looks good to me. The only question that I haven't seen an answer
> to from the maintainers is whether this is a __nonstring or not. It
> really looks like it should be a C String, so with that assumption:

To reaffirm the assumption, as I mentioned in my response to v1 these are
intended to be handled as C strings.

Acked-by: Tyrel Datwyler <tyreld@linux.ibm.com>

> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 
> -Kees
>