[v2] airo: replace deprecated strncpy with strscpy_pad

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

`extra` is clearly supposed to be NUL-terminated which is evident by the
manual NUL-byte assignment as well as its immediate usage with strlen().

Moreover, let's NUL-pad since there is deliberate effort (48 instances)
made elsewhere to zero-out buffers in these getters and setters:
6050 | memset(local->config.nodeName, 0, sizeof(local->config.nodeName));
6130 | memset(local->config.rates, 0, 8);
6139 | memset(local->config.rates, 0, 8);
6414 | memset(key.key, 0, MAX_KEY_SIZE);
6497 | memset(extra, 0, 16);
(to be clear, strncpy also NUL-padded -- we are matching that behavior)

Considering the above, a suitable replacement is `strscpy_pad` due to
the fact that it guarantees both NUL-termination and NUL-padding on the
destination buffer.

We can also replace the hard-coded size of "16" to IW_ESSID_MAX_SIZE
because this function is a wext handler.

In wext-core.c we have:
static const struct iw_ioctl_description standard_ioctl[] = {
...
        [IW_IOCTL_IDX(SIOCGIWNICKN)] = {
                .header_type    = IW_HEADER_TYPE_POINT,
                .token_size     = 1,
                .max_tokens     = IW_ESSID_MAX_SIZE,
        },

So the buffer size is (strangely) IW_ESSID_MAX_SIZE

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- use IW_ESSID_MAX_SIZE (thanks Jeff, Kees)
- Link to v1: https://lore.kernel.org/r/20231017-strncpy-drivers-net-wireless-cisco-airo-c-v1-1-e34d5b3b7e37@google.com
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/wireless/cisco/airo.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)


---
base-commit: 58720809f52779dc0f08e53e54b014209d13eebb
change-id: 20231017-strncpy-drivers-net-wireless-cisco-airo-c-d09cd0500a6e

Best regards,
--
Justin Stitt <justinstitt@google.com>

On 10/26/2023 4:19 PM, 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.
> 
> `extra` is clearly supposed to be NUL-terminated which is evident by the
> manual NUL-byte assignment as well as its immediate usage with strlen().
> 
> Moreover, let's NUL-pad since there is deliberate effort (48 instances)
> made elsewhere to zero-out buffers in these getters and setters:
> 6050 | memset(local->config.nodeName, 0, sizeof(local->config.nodeName));
> 6130 | memset(local->config.rates, 0, 8);
> 6139 | memset(local->config.rates, 0, 8);
> 6414 | memset(key.key, 0, MAX_KEY_SIZE);
> 6497 | memset(extra, 0, 16);
> (to be clear, strncpy also NUL-padded -- we are matching that behavior)
> 
> Considering the above, a suitable replacement is `strscpy_pad` due to
> the fact that it guarantees both NUL-termination and NUL-padding on the
> destination buffer.
> 
> We can also replace the hard-coded size of "16" to IW_ESSID_MAX_SIZE
> because this function is a wext handler.
> 
> In wext-core.c we have:
> static const struct iw_ioctl_description standard_ioctl[] = {
> ...
>          [IW_IOCTL_IDX(SIOCGIWNICKN)] = {
>                  .header_type    = IW_HEADER_TYPE_POINT,
>                  .token_size     = 1,
>                  .max_tokens     = IW_ESSID_MAX_SIZE,
>          },
> 
> So the buffer size is (strangely) IW_ESSID_MAX_SIZE
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>

Kees Cook <keescook@chromium.org> writes:

> On Thu, Oct 26, 2023 at 11:19:18PM +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.
>> 
>> `extra` is clearly supposed to be NUL-terminated which is evident by the
>> manual NUL-byte assignment as well as its immediate usage with strlen().
>> 
>> Moreover, let's NUL-pad since there is deliberate effort (48 instances)
>> made elsewhere to zero-out buffers in these getters and setters:
>> 6050 | memset(local->config.nodeName, 0, sizeof(local->config.nodeName));
>> 6130 | memset(local->config.rates, 0, 8);
>> 6139 | memset(local->config.rates, 0, 8);
>> 6414 | memset(key.key, 0, MAX_KEY_SIZE);
>> 6497 | memset(extra, 0, 16);
>> (to be clear, strncpy also NUL-padded -- we are matching that behavior)
>> 
>> Considering the above, a suitable replacement is `strscpy_pad` due to
>> the fact that it guarantees both NUL-termination and NUL-padding on the
>> destination buffer.
>> 
>> We can also replace the hard-coded size of "16" to IW_ESSID_MAX_SIZE
>> because this function is a wext handler.
>> 
>> In wext-core.c we have:
>> static const struct iw_ioctl_description standard_ioctl[] = {
>> ...
>>         [IW_IOCTL_IDX(SIOCGIWNICKN)] = {
>>                 .header_type    = IW_HEADER_TYPE_POINT,
>>                 .token_size     = 1,
>>                 .max_tokens     = IW_ESSID_MAX_SIZE,
>>         },
>> 
>> So the buffer size is (strangely) IW_ESSID_MAX_SIZE
>> 
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>> Link: https://github.com/KSPP/linux/issues/90
>> Cc: linux-hardening@vger.kernel.org
>> Signed-off-by: Justin Stitt <justinstitt@google.com>
>
> Looks good; thanks!
>
> Reviewed-by: Kees Cook <keescook@chromium.org>

BTW most likely next week this driver and a bunch of other ancient
drivers will removed:

https://patchwork.kernel.org/project/linux-wireless/list/?series=795639&state=*&order=date

So to avoid unnecessary work on already removed drivers I recommend
using wireless-next as the baseline for wireless patches. Though I'm
still planning to apply this patch in case we ever add the driver back
(I hope not).

Justin Stitt <justinstitt@google.com> 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.
> 
> `extra` is clearly supposed to be NUL-terminated which is evident by the
> manual NUL-byte assignment as well as its immediate usage with strlen().
> 
> Moreover, let's NUL-pad since there is deliberate effort (48 instances)
> made elsewhere to zero-out buffers in these getters and setters:
> 6050 | memset(local->config.nodeName, 0, sizeof(local->config.nodeName));
> 6130 | memset(local->config.rates, 0, 8);
> 6139 | memset(local->config.rates, 0, 8);
> 6414 | memset(key.key, 0, MAX_KEY_SIZE);
> 6497 | memset(extra, 0, 16);
> (to be clear, strncpy also NUL-padded -- we are matching that behavior)
> 
> Considering the above, a suitable replacement is `strscpy_pad` due to
> the fact that it guarantees both NUL-termination and NUL-padding on the
> destination buffer.
> 
> We can also replace the hard-coded size of "16" to IW_ESSID_MAX_SIZE
> because this function is a wext handler.
> 
> In wext-core.c we have:
> static const struct iw_ioctl_description standard_ioctl[] = {
> ...
>         [IW_IOCTL_IDX(SIOCGIWNICKN)] = {
>                 .header_type    = IW_HEADER_TYPE_POINT,
>                 .token_size     = 1,
>                 .max_tokens     = IW_ESSID_MAX_SIZE,
>         },
> 
> So the buffer size is (strangely) IW_ESSID_MAX_SIZE
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>

Patch applied to wireless-next.git, thanks.

9beac4ee4928 wifi: airo: replace deprecated strncpy with strscpy_pad