ipv6: mcast: extend RCU protection in igmp6_send()

igmp6_send() can be called without RTNL or RCU being held.

Extend RCU protection so that we can safely fetch the net pointer
and avoid a potential UAF.

Note that we no longer can use sock_alloc_send_skb() because
ipv6.igmp_sk uses GFP_KERNEL allocations which can sleep.

Instead use alloc_skb() and charge the net->ipv6.igmp_sk
socket under RCU protection.

Fixes: b8ad0cbc58f7 ("[NETNS][IPV6] mcast - handle several network namespace")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250207135841.1948589-9-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 9dfdb40988b0f8edd882c07b555ea0115ee95cab..81a739ebf7094694a6f5de5020cd4c4d1c9642d1 100644 (file)
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -2165,21 +2165,21 @@ static void mld_send_cr(struct inet6_dev *idev)
 
 static void igmp6_send(struct in6_addr *addr, struct net_device *dev, int type)
 {
-       struct net *net = dev_net(dev);
-       struct sock *sk = net->ipv6.igmp_sk;
+       const struct in6_addr *snd_addr, *saddr;
+       int err, len, payload_len, full_len;
+       struct in6_addr addr_buf;
        struct inet6_dev *idev;
        struct sk_buff *skb;
        struct mld_msg *hdr;
-       const struct in6_addr *snd_addr, *saddr;
-       struct in6_addr addr_buf;
        int hlen = LL_RESERVED_SPACE(dev);
        int tlen = dev->needed_tailroom;
-       int err, len, payload_len, full_len;
        u8 ra[8] = { IPPROTO_ICMPV6, 0,
                     IPV6_TLV_ROUTERALERT, 2, 0, 0,
                     IPV6_TLV_PADN, 0 };
-       struct flowi6 fl6;
        struct dst_entry *dst;
+       struct flowi6 fl6;
+       struct net *net;
+       struct sock *sk;
 
        if (type == ICMPV6_MGM_REDUCTION)
                snd_addr = &in6addr_linklocal_allrouters;
@@ -2190,19 +2190,21 @@ static void igmp6_send(struct in6_addr *addr, struct net_device *dev, int type)
        payload_len = len + sizeof(ra);
        full_len = sizeof(struct ipv6hdr) + payload_len;
 
-       rcu_read_lock();
-       IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_OUTREQUESTS);
-       rcu_read_unlock();
+       skb = alloc_skb(hlen + tlen + full_len, GFP_KERNEL);
 
-       skb = sock_alloc_send_skb(sk, hlen + tlen + full_len, 1, &err);
+       rcu_read_lock();
 
+       net = dev_net_rcu(dev);
+       idev = __in6_dev_get(dev);
+       IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTREQUESTS);
        if (!skb) {
-               rcu_read_lock();
-               IP6_INC_STATS(net, __in6_dev_get(dev),
-                             IPSTATS_MIB_OUTDISCARDS);
+               IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
                rcu_read_unlock();
                return;
        }
+       sk = net->ipv6.igmp_sk;
+       skb_set_owner_w(skb, sk);
+
        skb->priority = TC_PRIO_CONTROL;
        skb_reserve(skb, hlen);
 
@@ -2227,9 +2229,6 @@ static void igmp6_send(struct in6_addr *addr, struct net_device *dev, int type)
                                         IPPROTO_ICMPV6,
                                         csum_partial(hdr, len, 0));
 
-       rcu_read_lock();
-       idev = __in6_dev_get(skb->dev);
-
        icmpv6_flow_init(sk, &fl6, type,
                         &ipv6_hdr(skb)->saddr, &ipv6_hdr(skb)->daddr,
                         skb->dev->ifindex);