linux-hardening - Re: [PATCH] usbip: usbip_host: Replace strlcpy with strscpy

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Date:   Tue, 13 Jun 2023 12:31:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-hardening@...r.kernel.org, Hongren Zheng <i@...ithal.me>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usbip: usbip_host: Replace strlcpy with strscpy

On Tue, Jun 13, 2023 at 12:44:02AM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().
> 
> Direct replacement is safe here since return value of -E2BIG
> is used to check for truncation instead of sizeof(dest).
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> 
> Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
> ---
>  drivers/usb/usbip/stub_main.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c
> index e8c3131a8543..a92a284f5abb 100644
> --- a/drivers/usb/usbip/stub_main.c
> +++ b/drivers/usb/usbip/stub_main.c
> @@ -174,8 +174,8 @@ static ssize_t match_busid_store(struct device_driver *dev, const char *buf,
>  		return -EINVAL;
>  
>  	/* busid needs to include \0 termination */
> -	len = strlcpy(busid, buf + 4, BUSID_SIZE);
> -	if (sizeof(busid) <= len)
> +	len = strscpy(busid, buf + 4, BUSID_SIZE);
> +	if (len == -E2BIG)
>  		return -EINVAL;

"len" is never used again, so maybe:

	if (strscpy(...) < 0)
		return -EINVAL;

-Kees

>  
>  	if (!strncmp(buf, "add ", 4)) {
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 
> 

-- 
Kees Cook