netfilter: rpfilter/fib: Set ->flowic_uid correctly for user namespaces.

Currently netfilter's rpfilter and fib modules implicitely initialise
->flowic_uid with 0. This is normally the root UID. However, this isn't
the case in user namespaces, where user ID 0 is mapped to a different
kernel UID. By initialising ->flowic_uid with sock_net_uid(), we get
the root UID of the user namespace, thus keeping the same behaviour
whether or not we're running in a user namepspace.

Note, this is similar to commit 8bcfd0925e ("ipv4: add missing
initialization for flowi4_uid"), which fixed the rp_filter sysctl.

Fixes: 622ec2c9d5 ("net: core: add UID to flows, rules, and routes")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/ipt_rpfilter.c

@@ -78,6 +78,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	flow.flowi4_tos = iph->tos & IPTOS_RT_MASK;
 	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
 	flow.flowi4_l3mdev = l3mdev_master_ifindex_rcu(xt_in(par));
+	flow.flowi4_uid = sock_net_uid(xt_net(par), NULL);
 
 	return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
 }

net/ipv4/netfilter/nft_fib_ipv4.c

@@ -65,6 +65,7 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	struct flowi4 fl4 = {
 		.flowi4_scope = RT_SCOPE_UNIVERSE,
 		.flowi4_iif = LOOPBACK_IFINDEX,
+		.flowi4_uid = sock_net_uid(nft_net(pkt), NULL),
 	};
 	const struct net_device *oif;
 	const struct net_device *found;

net/ipv6/netfilter/ip6t_rpfilter.c

@@ -40,6 +40,7 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 		.flowi6_l3mdev = l3mdev_master_ifindex_rcu(dev),
 		.flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
 		.flowi6_proto = iph->nexthdr,
+		.flowi6_uid = sock_net_uid(net, NULL),
 		.daddr = iph->saddr,
 	};
 	int lookup_flags;

net/ipv6/netfilter/nft_fib_ipv6.c

@@ -66,6 +66,7 @@ static u32 __nft_fib6_eval_type(const struct nft_fib *priv,
 	struct flowi6 fl6 = {
 		.flowi6_iif = LOOPBACK_IFINDEX,
 		.flowi6_proto = pkt->tprot,
+		.flowi6_uid = sock_net_uid(nft_net(pkt), NULL),
 	};
 	u32 ret = 0;
 
@@ -163,6 +164,7 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	struct flowi6 fl6 = {
 		.flowi6_iif = LOOPBACK_IFINDEX,
 		.flowi6_proto = pkt->tprot,
+		.flowi6_uid = sock_net_uid(nft_net(pkt), NULL),
 	};
 	struct rt6_info *rt;
 	int lookup_flags;