netdev - Re: [PATCH nf-next 2/6] netfilter: bridge: check len before accessing more nh data

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Message-ID: <f7tttyw4dk4.fsf@redhat.com>
Date:   Tue, 07 Mar 2023 13:32:59 -0500
From:   Aaron Conole <aconole@...hat.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     netfilter-devel@...r.kernel.org,
        network dev <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>, davem@...emloft.net,
        kuba@...nel.org, Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Pravin B Shelar <pshelar@....org>
Subject: Re: [PATCH nf-next 2/6] netfilter: bridge: check len before
 accessing more nh data

Xin Long <lucien.xin@...il.com> writes:

> In the while loop of br_nf_check_hbh_len(), similar to ip6_parse_tlv(),
> before accessing 'nh[off + 1]', it should add a check 'len < 2'; and
> before parsing IPV6_TLV_JUMBO, it should add a check 'optlen > len',
> in case of overflows.
>
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---

Reviewed-by: Aaron Conole <aconole@...hat.com>

>  net/bridge/br_netfilter_ipv6.c | 47 ++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 25 deletions(-)
>
> diff --git a/net/bridge/br_netfilter_ipv6.c b/net/bridge/br_netfilter_ipv6.c
> index 5cd3e4c35123..50f564c33551 100644
> --- a/net/bridge/br_netfilter_ipv6.c
> +++ b/net/bridge/br_netfilter_ipv6.c
> @@ -50,54 +50,51 @@ static int br_nf_check_hbh_len(struct sk_buff *skb)
>  	u32 pkt_len;
>  
>  	if (!pskb_may_pull(skb, off + 8))
> -		goto bad;
> +		return -1;
>  	nh = (u8 *)(ipv6_hdr(skb) + 1);
>  	len = (nh[1] + 1) << 3;
>  
>  	if (!pskb_may_pull(skb, off + len))
> -		goto bad;
> +		return -1;
>  	nh = skb_network_header(skb);
>  
>  	off += 2;
>  	len -= 2;
> -
>  	while (len > 0) {
> -		int optlen = nh[off + 1] + 2;
> -
> -		switch (nh[off]) {
> -		case IPV6_TLV_PAD1:
> -			optlen = 1;
> -			break;
> +		int optlen;
>  
> -		case IPV6_TLV_PADN:
> -			break;
> +		if (nh[off] == IPV6_TLV_PAD1) {
> +			off++;
> +			len--;
> +			continue;
> +		}
> +		if (len < 2)
> +			return -1;
> +		optlen = nh[off + 1] + 2;
> +		if (optlen > len)
> +			return -1;
>  
> -		case IPV6_TLV_JUMBO:
> +		if (nh[off] == IPV6_TLV_JUMBO) {
>  			if (nh[off + 1] != 4 || (off & 3) != 2)
> -				goto bad;
> +				return -1;
>  			pkt_len = ntohl(*(__be32 *)(nh + off + 2));
>  			if (pkt_len <= IPV6_MAXPLEN ||
>  			    ipv6_hdr(skb)->payload_len)
> -				goto bad;
> +				return -1;
>  			if (pkt_len > skb->len - sizeof(struct ipv6hdr))
> -				goto bad;
> +				return -1;
>  			if (pskb_trim_rcsum(skb,
>  					    pkt_len + sizeof(struct ipv6hdr)))
> -				goto bad;
> +				return -1;
>  			nh = skb_network_header(skb);
> -			break;
> -		default:
> -			if (optlen > len)
> -				goto bad;
> -			break;
>  		}
>  		off += optlen;
>  		len -= optlen;
>  	}
> -	if (len == 0)
> -		return 0;
> -bad:
> -	return -1;
> +	if (len)
> +		return -1;
> +
> +	return 0;
>  }
>  
>  int br_validate_ipv6(struct net *net, struct sk_buff *skb)