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SubjectRe: [PATCH] airo: replace deprecated strncpy with strscpy_pad
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On 10/17/2023 2:12 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.
>
> Technically, we can now copy one less byte into `extra` as we cannot
> determine the sizeof `extra` at compile time and the hard-coded value of
> 16 means that strscpy_pad() will automatically truncate and set the byte
> at offset 15 to NUL. However, the current code manually sets a
> NUL-byte at offset 16. If this is an issue, the solution is to change
> the hard-coded magic number to 17 instead of 16. I didn't do this in
> this patch because a hard-coded 17 seems bad (even more so than 16).

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 if you want to use
that for the buffer 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>
> ---
> 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..8cfb1de5933e 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, 16);
> 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@google.com>
>

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