[PATCH nf] netfilter: rpfilter/fib: Set ->flowic_uid correctly for user namespaces.

[PATCH nf] netfilter: rpfilter/fib: Set ->flowic_uid correctly for user namespaces.

[Guillaume Nault]

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 8bcfd0925ef1 ("ipv4: add missing
initialization for flowi4_uid"), which fixed the rp_filter sysctl.

Fixes: 622ec2c9d524 ("net: core: add UID to flows, rules, and routes")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
 net/ipv4/netfilter/ipt_rpfilter.c  | 1 +
 net/ipv4/netfilter/nft_fib_ipv4.c  | 1 +
 net/ipv6/netfilter/ip6t_rpfilter.c | 1 +
 net/ipv6/netfilter/nft_fib_ipv6.c  | 2 ++
 4 files changed, 5 insertions(+)

diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
index ff85db52b2e5..ded5bef02f77 100644
--- a/net/ipv4/netfilter/ipt_rpfilter.c
+++ b/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;
 }
diff --git a/net/ipv4/netfilter/nft_fib_ipv4.c b/net/ipv4/netfilter/nft_fib_ipv4.c
index e886147eed11..fc65d69f23e1 100644
--- a/net/ipv4/netfilter/nft_fib_ipv4.c
+++ b/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;
diff --git a/net/ipv6/netfilter/ip6t_rpfilter.c b/net/ipv6/netfilter/ip6t_rpfilter.c
index 69d86b040a6a..a01d9b842bd0 100644
--- a/net/ipv6/netfilter/ip6t_rpfilter.c
+++ b/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;
diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c
index 91faac610e03..36dc14b34388 100644
--- a/net/ipv6/netfilter/nft_fib_ipv6.c
+++ b/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;
-- 
2.21.3

Re: [PATCH nf] netfilter: rpfilter/fib: Set ->flowic_uid correctly for user namespaces.

[Pablo Neira Ayuso]

On Thu, Oct 13, 2022 at 04:37:47PM +0200, Guillaume Nault wrote:
> 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 8bcfd0925ef1 ("ipv4: add missing
> initialization for flowi4_uid"), which fixed the rp_filter sysctl.

Applied, thanks