linux-kernel - Re: [PATCH v1 1/2] mmc-utils: Use memcpy instead of strncpy

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Date:   Mon, 15 Nov 2021 12:39:15 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     Bean Huo <huobean@...il.com>
Cc:     ulf.hansson@...aro.org, adrian.hunter@...el.com,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        beanhuo@...ron.com
Subject: Re: [PATCH v1 1/2] mmc-utils: Use memcpy instead of strncpy

Hi Bean.

> -               strncpy(lbuf, (char*)&ext_csd[EXT_CSD_FIRMWARE_VERSION], 8);
> +               memcpy(lbuf, (char*)&ext_csd[EXT_CSD_FIRMWARE_VERSION], 8);
> +               lbuf[8] = '\0';

Above copies exactly 8 bytes, without any regard to the sizes of
destination-buffer (lbuf) or source-buffer (ext_csd). Thus, there are
high chances of overflow/underflow/out-of-bounds.

If ext_csd contains, say a string 5 characters long, you would want to
copy 6 characters (5 for length, 1 for null-terminator).

I guess you are trying to copy as-many-bytes as possible to lbuf,
including the null-character.
Thus, strlcpy/strscpy should be used here.

Something like :

strlcpy(lbuf, (char*)&ext_csd[EXT_CSD_FIRMWARE_VERSION], sizeof(lbuf));
or
strscpy(lbuf, (char*)&ext_csd[EXT_CSD_FIRMWARE_VERSION], sizeof(lbuf));

Note that you do not need to worry about putting the null-terminator.
strlcpy/strscpy already take care of that for you.

Thanks and Regards,
Ajay