[PATCH v2] airo: replace deprecated strncpy with strscpy_pad

[Justin Stitt]

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@xxxxxxxxxxxxxxx
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
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@xxxxxxxxxx
---
Note: build-tested only.

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

diff --git a/drivers/net/wireless/cisco/airo.c b/drivers/net/wireless/cisco/airo.c
index dbd13f7aa3e6..6a099642e854 100644
--- a/drivers/net/wireless/cisco/airo.c
+++ b/drivers/net/wireless/cisco/airo.c
@@ -6067,8 +6067,7 @@ static int airo_get_nick(struct net_device *dev,
 	struct airo_info *local = dev->ml_priv;
 
 	readConfigRid(local, 1);
-	strncpy(extra, local->config.nodeName, 16);
-	extra[16] = '\0';
+	strscpy_pad(extra, local->config.nodeName, IW_ESSID_MAX_SIZE);
 	dwrq->length = strlen(extra);
 
 	return 0;

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

Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>