linux-hardening - Re: [PATCH] drm/i2c: tda998x: Replace all non-returning strlcpy with strscpy

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Message-ID: <ZGuSeZcLfXNyCqtv@shell.armlinux.org.uk>
Date:   Mon, 22 May 2023 17:04:09 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/i2c: tda998x: Replace all non-returning strlcpy with
 strscpy

On Mon, May 22, 2023 at 03:53:50PM +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().
> No return values were used, so direct replacement is safe.
...
>  	memset(&cec_info, 0, sizeof(cec_info));
> -	strlcpy(cec_info.type, "tda9950", sizeof(cec_info.type));
> +	strscpy(cec_info.type, "tda9950", sizeof(cec_info.type));

Please explain how:

1) a C string can not be NUL terminated.
2) this source string could be longer than I2C_NAME_SIZE (20 bytes)
   which is unlikely to ever shrink.

I'm not saying I disagree with the patch, but the boilerplate commit
message isn't correct for this change, and is actually misleading
for what the patch actually is.

-- 
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