linux-kernel - RE: [PATCH] powerpc: use strscpy to copy strings

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Message-ID: <c82f01143a174c8281930158e4804a4b@AcuMS.aculab.com>
Date:   Mon, 20 Dec 2021 10:23:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jason Wang' <wangborong@...rlc.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>
CC:     "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] powerpc: use strscpy to copy strings

From: Jason Wang
> Sent: 20 December 2021 03:24
> 
> The strlcpy should not be used because it doesn't limit the source
> length. So that it will lead some potential bugs.
> 
> But the strscpy doesn't require reading memory from the src string
> beyond the specified "count" bytes, and since the return value is
> easier to error-check than strlcpy()'s. In addition, the implementation
> is robust to the string changing out from underneath it, unlike the
> current strlcpy() implementation.
> 
> Thus, replace strlcpy with strscpy.
> 
> Signed-off-by: Jason Wang <wangborong@...rlc.com>
> ---
>  arch/powerpc/platforms/pasemi/misc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pasemi/misc.c b/arch/powerpc/platforms/pasemi/misc.c
> index 1bf65d02d3ba..06a1ffd43bfe 100644
> --- a/arch/powerpc/platforms/pasemi/misc.c
> +++ b/arch/powerpc/platforms/pasemi/misc.c
> @@ -35,7 +35,7 @@ static int __init find_i2c_driver(struct device_node *node,
>  	for (i = 0; i < ARRAY_SIZE(i2c_devices); i++) {
>  		if (!of_device_is_compatible(node, i2c_devices[i].of_device))
>  			continue;
> -		if (strlcpy(info->type, i2c_devices[i].i2c_type,
> +		if (strscpy(info->type, i2c_devices[i].i2c_type,
>  			    I2C_NAME_SIZE) >= I2C_NAME_SIZE)
>  			return -ENOMEM;

Isn't that the wrong overflow check?
Doesn't strscpy() return a -ve errno value on failure
(just to cause a different buffer overflow issue?)

Not that any kind of overflow is actually possible in that over-engineered
code fragment.

	David

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