netdev - [PATCH net 7/8] ndisc: extend RCU protection in ndisc_send

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Message-ID: <20250207135841.1948589-8-edumazet@google.com>
Date: Fri,  7 Feb 2025 13:58:39 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Simon Horman <horms@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 7/8] ndisc: extend RCU protection in ndisc_send_skb()

ndisc_send_skb() can be called without RTNL or RCU held.

Acquire rcu_read_lock() earlier, so that we can use dev_net_rcu()
and avoid a potential UAF.

Fixes: 1762f7e88eb3 ("[NETNS][IPV6] ndisc - make socket control per namespace")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/ndisc.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 90f8aa2d7af2ec1103220378c155b7b724efc575..8699d1a188dc4a15ac0b65229c4dd19240c9c054 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -471,16 +471,20 @@ static void ip6_nd_hdr(struct sk_buff *skb,
 void ndisc_send_skb(struct sk_buff *skb, const struct in6_addr *daddr,
 		    const struct in6_addr *saddr)
 {
+	struct icmp6hdr *icmp6h = icmp6_hdr(skb);
 	struct dst_entry *dst = skb_dst(skb);
-	struct net *net = dev_net(skb->dev);
-	struct sock *sk = net->ipv6.ndisc_sk;
 	struct inet6_dev *idev;
+	struct net *net;
+	struct sock *sk;
 	int err;
-	struct icmp6hdr *icmp6h = icmp6_hdr(skb);
 	u8 type;
 
 	type = icmp6h->icmp6_type;
 
+	rcu_read_lock();
+
+	net = dev_net_rcu(skb->dev);
+	sk = net->ipv6.ndisc_sk;
 	if (!dst) {
 		struct flowi6 fl6;
 		int oif = skb->dev->ifindex;
@@ -488,6 +492,7 @@ void ndisc_send_skb(struct sk_buff *skb, const struct in6_addr *daddr,
 		icmpv6_flow_init(sk, &fl6, type, saddr, daddr, oif);
 		dst = icmp6_dst_alloc(skb->dev, &fl6);
 		if (IS_ERR(dst)) {
+			rcu_read_unlock();
 			kfree_skb(skb);
 			return;
 		}
@@ -502,7 +507,6 @@ void ndisc_send_skb(struct sk_buff *skb, const struct in6_addr *daddr,
 
 	ip6_nd_hdr(skb, saddr, daddr, READ_ONCE(inet6_sk(sk)->hop_limit), skb->len);
 
-	rcu_read_lock();
 	idev = __in6_dev_get(dst->dev);
 	IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTREQUESTS);
 
-- 
2.48.1.502.g6dc24dfdaf-goog