linux-kernel - Re: [PATCH v2] airo: replace deprecated strncpy with strscpy

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Message-ID: <202310270859.8EB5599A@keescook>
Date:   Fri, 27 Oct 2023 08:59:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] airo: replace deprecated strncpy with strscpy_pad

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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Looks good; thanks!

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

-- 
Kees Cook