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Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, gunho.lee@lge.com, stable@vger.kernel.org, Sasha Levin , Greg Kroah-Hartman , Eric Dumazet , Chanho Min , Jakub Kicinski Subject: [PATCH] ipv6: mcast: extend RCU protection in igmp6_send() Date: Mon, 18 Aug 2025 18:24:53 +0900 Message-Id: <20250818092453.38281-1-chanho.min@lge.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Eric Dumazet [ 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 namespac= e") Signed-off-by: Eric Dumazet Reviewed-by: David Ahern Reviewed-by: Kuniyuki Iwashima 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 OutForwDatagr= ams), so IPSTATS_MIB_OUTREQUESTS was changed to IPSTATS_MIB_OUTPKGS defined as 'OutRequests'. ] Signed-off-by: Chanho Min Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- 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) =20 static void igmp6_send(struct in6_addr *addr, struct net_device *dev, int = type) { - struct net *net =3D dev_net(dev); - struct sock *sk =3D 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 =3D LL_RESERVED_SPACE(dev); int tlen =3D dev->needed_tailroom; - int err, len, payload_len, full_len; u8 ra[8] =3D { 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; =20 if (type =3D=3D ICMPV6_MGM_REDUCTION) snd_addr =3D &in6addr_linklocal_allrouters; @@ -2002,20 +2002,21 @@ static void igmp6_send(struct in6_addr *addr, struc= t net_device *dev, int type) payload_len =3D len + sizeof(ra); full_len =3D sizeof(struct ipv6hdr) + payload_len; =20 - rcu_read_lock(); - IP6_UPD_PO_STATS(net, __in6_dev_get(dev), - IPSTATS_MIB_OUT, full_len); - rcu_read_unlock(); + skb =3D alloc_skb(hlen + tlen + full_len, GFP_KERNEL); =20 - skb =3D sock_alloc_send_skb(sk, hlen + tlen + full_len, 1, &err); + rcu_read_lock(); =20 + net =3D dev_net_rcu(dev); + idev =3D __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 =3D net->ipv6.igmp_sk; + skb_set_owner_w(skb, sk); + skb->priority =3D TC_PRIO_CONTROL; skb_reserve(skb, hlen); =20 @@ -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)); =20 - rcu_read_lock(); - idev =3D __in6_dev_get(skb->dev); - icmpv6_flow_init(sk, &fl6, type, &ipv6_hdr(skb)->saddr, &ipv6_hdr(skb)->daddr, skb->dev->ifindex);