netdev - [PATCH v2 net-next 06/15] ipv6: mcast: Don't hold RTNL for IPV6_ADD_MEMBERSHIP and MCAST_JOIN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250624202616.526600-7-kuni1840@gmail.com>
Date: Tue, 24 Jun 2025 13:24:12 -0700
From: Kuniyuki Iwashima <kuni1840@...il.com>
To: "David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Kuniyuki Iwashima <kuni1840@...il.com>,
	netdev@...r.kernel.org
Subject: [PATCH v2 net-next 06/15] ipv6: mcast: Don't hold RTNL for IPV6_ADD_MEMBERSHIP and MCAST_JOIN_GROUP.

From: Kuniyuki Iwashima <kuniyu@...gle.com>

In __ipv6_sock_mc_join(), per-socket mld data is protected by lock_sock(),
and only __dev_get_by_index() requires RTNL.

Let's use dev_get_by_index() and drop RTNL for IPV6_ADD_MEMBERSHIP and
MCAST_JOIN_GROUP.

Note that we must call rt6_lookup() and dev_hold() under RCU.

If rt6_lookup() returns an entry from the exception table, dst_dev_put()
could change rt->dev.dst to loopback concurrently, and the original device
could lose the refcount before dev_hold() and unblock device registration.

dst_dev_put() is called from NETDEV_UNREGISTER and synchronize_net() follows
it, so as long as rt6_lookup() and dev_hold() are called within the same
RCU critical section, the dev is alive.

Even if the race happens, they are synchronised by idev->dead and mcast
addresses are cleaned up.

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
v2: Hold rcu_read_lock() around rt6_lookup & dev_hold()
---
 net/ipv6/ipv6_sockglue.c |  2 --
 net/ipv6/mcast.c         | 22 ++++++++++++----------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 1e225e6489ea..cb0dc885cbe4 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -121,11 +121,9 @@ static bool setsockopt_needs_rtnl(int optname)
 {
 	switch (optname) {
 	case IPV6_ADDRFORM:
-	case IPV6_ADD_MEMBERSHIP:
 	case IPV6_DROP_MEMBERSHIP:
 	case IPV6_JOIN_ANYCAST:
 	case IPV6_LEAVE_ANYCAST:
-	case MCAST_JOIN_GROUP:
 	case MCAST_LEAVE_GROUP:
 	case MCAST_JOIN_SOURCE_GROUP:
 	case MCAST_LEAVE_SOURCE_GROUP:
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index b3f063b5ffd7..9fc7672926bf 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -175,14 +175,12 @@ static int unsolicited_report_interval(struct inet6_dev *idev)
 static int __ipv6_sock_mc_join(struct sock *sk, int ifindex,
 			       const struct in6_addr *addr, unsigned int mode)
 {
-	struct net_device *dev = NULL;
-	struct ipv6_mc_socklist *mc_lst;
 	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_mc_socklist *mc_lst;
 	struct net *net = sock_net(sk);
+	struct net_device *dev = NULL;
 	int err;
 
-	ASSERT_RTNL();
-
 	if (!ipv6_addr_is_multicast(addr))
 		return -EINVAL;
 
@@ -202,13 +200,18 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex,
 
 	if (ifindex == 0) {
 		struct rt6_info *rt;
+
+		rcu_read_lock();
 		rt = rt6_lookup(net, addr, NULL, 0, NULL, 0);
 		if (rt) {
 			dev = rt->dst.dev;
+			dev_hold(dev);
 			ip6_rt_put(rt);
 		}
-	} else
-		dev = __dev_get_by_index(net, ifindex);
+		rcu_read_unlock();
+	} else {
+		dev = dev_get_by_index(net, ifindex);
+	}
 
 	if (!dev) {
 		sock_kfree_s(sk, mc_lst, sizeof(*mc_lst));
@@ -219,12 +222,11 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex,
 	mc_lst->sfmode = mode;
 	RCU_INIT_POINTER(mc_lst->sflist, NULL);
 
-	/*
-	 *	now add/increase the group membership on the device
-	 */
-
+	/* now add/increase the group membership on the device */
 	err = __ipv6_dev_mc_inc(dev, addr, mode);
 
+	dev_put(dev);
+
 	if (err) {
 		sock_kfree_s(sk, mc_lst, sizeof(*mc_lst));
 		return err;
-- 
2.49.0