From: Eric Dumazet edumazet@google.com

[ Upstream commit 087c1faa594fa07a66933d750c0b2610aa1a2946 ]

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.

Cc: stable@vger.kernel.org # 5.4 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 [ chanho: Backports to v5.4.y. v5.4.y does not include commit b4a11b2033b7(net: fix IPSTATS_MIB_OUTPKGS increment in OutForwDatagrams), so IPSTATS_MIB_OUTREQUESTS was changed to IPSTATS_MIB_OUTPKGS defined as 'OutRequests'. ] Signed-off-by: Chanho Min chanho.min@lge.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv6/mcast.c | 32 +++++++++++++++----------------- 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c index 7d0a6a7c9d283..c2dc70a69be94 100644 --- a/net/ipv6/mcast.c +++ b/net/ipv6/mcast.c @@ -1977,21 +1977,21 @@ 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; @@ -2002,20 +2002,21 @@ 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_UPD_PO_STATS(net, __in6_dev_get(dev), - IPSTATS_MIB_OUT, full_len); - 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_OUTPKTS); 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);

@@ -2040,9 +2041,6 @@ 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);