RE: [PATCH linux-next] arm64/idreg: use strscpy() is more robust and safer

From: David Laight <David.Laight@ACULAB.COM>
To: 'Will Deacon' <will@kernel.org>,
	"xu.panda668@gmail.com" <xu.panda668@gmail.com>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"maz@kernel.org" <maz@kernel.org>,
	"kristina.martsenko@arm.com" <kristina.martsenko@arm.com>,
	"vladimir.murzin@arm.com" <vladimir.murzin@arm.com>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"cgel.zte@gmail.com" <cgel.zte@gmail.com>,
	"Xu Panda" <xu.panda@zte.com.cn>, Zeal Robot <zealci@zte.com.cn>
Subject: RE: [PATCH linux-next] arm64/idreg: use strscpy() is more robust and safer
Date: Wed, 5 Oct 2022 13:57:34 +0000	[thread overview]
Message-ID: <8533a82ace484fe4ab73fccea7dc009b@AcuMS.aculab.com> (raw)
In-Reply-To: <20221004114818.GA23663@willie-the-truck>

From: Will Deacon
> Sent: 04 October 2022 12:48
> 
> On Thu, Sep 29, 2022 at 07:29:06AM +0000, xu.panda668@gmail.com wrote:
> > From: Xu Panda <xu.panda@zte.com.cn>
> >
> > The implementation of strscpy() is more robust and safer.
> > That's now the recommended way to copy NUL terminated strings.

In this case the input string isn't NUL terminated....

> >
> > Reported-by: Zeal Robot <zealci@zte.com.cn>
> > Signed-off-by: Xu Panda <xu.panda@zte.com.cn>
> > Signed-off-by: Xu Panda <xu.panda668@gmail.com>
> > ---
> >  arch/arm64/kernel/idreg-override.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> > index 95133765ed29..61bbec7ef62e 100644
> > --- a/arch/arm64/kernel/idreg-override.c
> > +++ b/arch/arm64/kernel/idreg-override.c
> > @@ -246,7 +246,7 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
> >                         return;
> >
> >                 len = min(len, ARRAY_SIZE(buf) - 1);
> > -               strncpy(buf, cmdline, len);
> > +               strscpy(buf, cmdline, len);
> >                 buf[len] = 0;
> 
> Aren't we terminating the buffer explicitly here anyway?

I doubt the code was tested.
It is always wrong regardless of the initial value of 'len'.

I think using strscpy() will delete the last character
and always add two '\0'.

On the face of it, that could probably be a memcpy().

But with the checks you don't need any of the length
checks that memcpy() might be gaining.

OTOH, if the code used parameqn() a few lines lower the
entire copy could be removed.

	David

-
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