netdev - Re: [PATCH RESEND nf-next] netfilter: add support for matching IPv4 options

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Message-ID: <20190619171832.om7losybbkysuk4r@salvia>
Date:   Wed, 19 Jun 2019 19:18:32 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Stephen Suryaputra <ssuryaextr@...il.com>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH RESEND nf-next] netfilter: add support for matching IPv4
 options

On Tue, Jun 11, 2019 at 08:09:12AM -0400, Stephen Suryaputra wrote:
[...]
> diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
> index a940c9fd9045..4155a32fade7 100644
> --- a/net/netfilter/nft_exthdr.c
> +++ b/net/netfilter/nft_exthdr.c
[...]
> +static int ipv4_find_option(struct net *net, struct sk_buff *skb,
> +			    unsigned int *offset, int target,
> +			    unsigned short *fragoff, int *flags)
> +{
[...]
> +	switch (target) {
> +	case IPOPT_SSRR:
> +	case IPOPT_LSRR:
[...]
> +	case IPOPT_RR:
[...]
> +	case IPOPT_RA:
[...]
> +	default:
> +		/* Either not supported or not a specific search, treated as
> +		 * found
> +		 */
> +		found = true;
> +		if (target >= 0) {
> +			target = -EOPNOTSUPP;
> +			break;
> +		}

Rules with this options will load fine:

ip option eol type 1
ip option noop type 1
ip option sec type 1
ip option timestamp type 1
ip option rr type 1
ip option sid type 1

However, they will not ever match I think.

found is set to true, but target is set to EOPNOTSUPP, then...

[...]
> +static void nft_exthdr_ipv4_eval(const struct nft_expr *expr,
> +				 struct nft_regs *regs,
> +				 const struct nft_pktinfo *pkt)
> +{
> +	struct nft_exthdr *priv = nft_expr_priv(expr);
> +	u32 *dest = &regs->data[priv->dreg];
> +	struct sk_buff *skb = pkt->skb;
> +	unsigned int offset;
> +	int err;
> +
> +	if (skb->protocol != htons(ETH_P_IP))
> +		goto err;
> +
> +	err = ipv4_find_option(nft_net(pkt), skb, &offset, priv->type, NULL, NULL);

... ipv4_find_option() returns -EOPNOTSUPP which says header does
not exist.

> +	if (priv->flags & NFT_EXTHDR_F_PRESENT) {
> +		*dest = (err >= 0);
> +		return;
> +	} else if (err < 0) {
> +		goto err;
> +	}