ipv6: mcast: add RCU protection to mld_newpack()

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

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>
Link: https://patch.msgid.link/20250212141021.1663666-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 81a739ebf7094694a6f5de5020cd4c4d1c9642d1..65831b4fee1fda1be110cf3f7d5abebaf076694d 100644 (file)
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1773,21 +1773,19 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
        struct net_device *dev = idev->dev;
        int hlen = LL_RESERVED_SPACE(dev);
        int tlen = dev->needed_tailroom;
-       struct net *net = dev_net(dev);
        const struct in6_addr *saddr;
        struct in6_addr addr_buf;
        struct mld2_report *pmr;
        struct sk_buff *skb;
        unsigned int size;
        struct sock *sk;
-       int err;
+       struct net *net;
 
-       sk = net->ipv6.igmp_sk;
        /* we assume size > sizeof(ra) here
         * Also try to not allocate high-order pages for big MTU
         */
        size = min_t(int, mtu, PAGE_SIZE / 2) + hlen + tlen;
-       skb = sock_alloc_send_skb(sk, size, 1, &err);
+       skb = alloc_skb(size, GFP_KERNEL);
        if (!skb)
                return NULL;
 
@@ -1795,6 +1793,12 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
        skb_reserve(skb, hlen);
        skb_tailroom_reserve(skb, mtu, tlen);
 
+       rcu_read_lock();
+
+       net = dev_net_rcu(dev);
+       sk = net->ipv6.igmp_sk;
+       skb_set_owner_w(skb, sk);
+
        if (ipv6_get_lladdr(dev, &addr_buf, IFA_F_TENTATIVE)) {
                /* <draft-ietf-magma-mld-source-05.txt>:
                 * use unspecified address as the source address
@@ -1806,6 +1810,8 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
 
        ip6_mc_hdr(sk, skb, dev, saddr, &mld2_all_mcr, NEXTHDR_HOP, 0);
 
+       rcu_read_unlock();
+
        skb_put_data(skb, ra, sizeof(ra));
 
        skb_set_transport_header(skb, skb_tail_pointer(skb) - skb->data);