linux-kernel - RE: [PATCH] netlink: don't copy over empty attribute data

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Date:	Wed, 22 Oct 2014 08:55:51 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Sasha Levin' <sasha.levin@...cle.com>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"a.ryabinin@...sung.com" <a.ryabinin@...sung.com>,
	"pablo@...filter.org" <pablo@...filter.org>,
	"mschmidt@...hat.com" <mschmidt@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH] netlink: don't copy over empty attribute data

From: Sasha Levin
> netlink uses empty data to seperate different levels. However, we still
> try to copy that data from a NULL ptr using memcpy, which is an undefined
> behaviour.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> ---
>  lib/nlattr.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/nlattr.c b/lib/nlattr.c
> index 9c3e85f..6512b43 100644
> --- a/lib/nlattr.c
> +++ b/lib/nlattr.c
> @@ -430,7 +430,8 @@ void __nla_put(struct sk_buff *skb, int attrtype, int attrlen,
>  	struct nlattr *nla;
> 
>  	nla = __nla_reserve(skb, attrtype, attrlen);
> -	memcpy(nla_data(nla), data, attrlen);
> +	if (data)
> +		memcpy(nla_data(nla), data, attrlen);

Were it even appropriate to add a conditional here, the correct
check would be against 'attrlen', not 'data'.

	David

>  }
>  EXPORT_SYMBOL(__nla_put);
> 
> --
> 1.7.10.4
> 
> --
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