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netfilter: nft_fib: reverse path filter for policy-based routing on iif

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If policy-based routing using the iif selector is used, then the fib
expression fails to look up for the reverse path from the prerouting
hook because the input interface cannot be inferred. In order to support
this scenario, extend the fib expression to allow to use after the route
lookup, from the forward hook.

This patch also adds support for the input hook for usability reasons.
Since the prerouting hook cannot be used for the scenario described
above, users need two rules: one for the forward chain and another rule
for the input chain to check for the reverse path check for locally
targeted traffic.

Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2022-03-31 17:14:47 +02:00
parent 00bd435208
commit be8be04e5d
3 changed files with 12 additions and 0 deletions
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4
net/ipv4/netfilter/nft_fib_ipv4.c
View File

@ -112,6 +112,10 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
fl4.daddr = iph->daddr;
fl4.saddr = get_saddr(iph->saddr);
} else {
if (nft_hook(pkt) == NF_INET_FORWARD &&
priv->flags & NFTA_FIB_F_IIF)
fl4.flowi4_iif = nft_out(pkt)->ifindex;
fl4.daddr = iph->saddr;
fl4.saddr = get_saddr(iph->daddr);
}

4
net/ipv6/netfilter/nft_fib_ipv6.c
View File

@ -30,6 +30,10 @@ static int nft_fib6_flowi_init(struct flowi6 *fl6, const struct nft_fib *priv,
fl6->daddr = iph->daddr;
fl6->saddr = iph->saddr;
} else {
if (nft_hook(pkt) == NF_INET_FORWARD &&
priv->flags & NFTA_FIB_F_IIF)
fl6->flowi6_iif = nft_out(pkt)->ifindex;
fl6->daddr = iph->saddr;
fl6->saddr = iph->daddr;
}

4
net/netfilter/nft_fib.c
View File

@ -35,6 +35,10 @@ int nft_fib_validate(const struct nft_ctx *ctx, const struct nft_expr *expr,
case NFT_FIB_RESULT_OIF:
case NFT_FIB_RESULT_OIFNAME:
hooks = (1 << NF_INET_PRE_ROUTING);
if (priv->flags & NFTA_FIB_F_IIF) {
hooks |= (1 << NF_INET_LOCAL_IN) |
(1 << NF_INET_FORWARD);
}
break;
case NFT_FIB_RESULT_ADDRTYPE:
if (priv->flags & NFTA_FIB_F_IIF)