netdev - [PATCH v1 net-next 03/15] ipv6: mcast: Check inet6_dev->dead under idev->mc_lock in __ipv6_dev_mc

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: <20250616233417.1153427-4-kuni1840@gmail.com>
Date: Mon, 16 Jun 2025 16:28:32 -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 v1 net-next 03/15] ipv6: mcast: Check inet6_dev->dead under idev->mc_lock in __ipv6_dev_mc_inc().

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

Since commit 63ed8de4be81 ("mld: add mc_lock for protecting
per-interface mld data"), every multicast resource is protected
by inet6_dev->mc_lock.

RTNL is unnecessary in terms of protection but still needed for
synchronisation between addrconf_ifdown() and __ipv6_dev_mc_inc().

Once we removed RTNL, there would be a race below, where we could
add a multicast address to a dead inet6_dev.

  CPU1                            CPU2
  ====                            ====
  addrconf_ifdown()               __ipv6_dev_mc_inc()
                                    if (idev->dead) <-- false
    dead = true                       return -ENODEV;
    ipv6_mc_destroy_dev() / ipv6_mc_down()
      mutex_lock(&idev->mc_lock)
      ...
      mutex_unlock(&idev->mc_lock)
                                    mutex_lock(&idev->mc_lock)
                                    ...
                                    mutex_unlock(&idev->mc_lock)

The race window can be easily closed by checking inet6_dev->dead
under inet6_dev->mc_lock in __ipv6_dev_mc_inc() as addrconf_ifdown()
will acquire it after marking inet6_dev dead.

Let's check inet6_dev->dead under mc_lock in __ipv6_dev_mc_inc().

Note that now __ipv6_dev_mc_inc() no longer depends on RTNL and
we can remove ASSERT_RTNL() there and the RTNL comment above
addrconf_join_solict().

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
 net/ipv6/addrconf.c |  7 +++----
 net/ipv6/mcast.c    | 11 +++++------
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ba2ec7c870cc..e4c48638211b 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2229,13 +2229,12 @@ void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp)
 	in6_ifa_put(ifp);
 }
 
-/* Join to solicited addr multicast group.
- * caller must hold RTNL */
+/* Join to solicited addr multicast group. */
 void addrconf_join_solict(struct net_device *dev, const struct in6_addr *addr)
 {
 	struct in6_addr maddr;
 
-	if (dev->flags&(IFF_LOOPBACK|IFF_NOARP))
+	if (READ_ONCE(dev->flags) & (IFF_LOOPBACK | IFF_NOARP))
 		return;
 
 	addrconf_addr_solict_mult(addr, &maddr);
@@ -3865,7 +3864,7 @@ static int addrconf_ifdown(struct net_device *dev, bool unregister)
 	 *	   Do not dev_put!
 	 */
 	if (unregister) {
-		idev->dead = 1;
+		WRITE_ONCE(idev->dead, 1);
 
 		/* protected by rtnl_lock */
 		RCU_INIT_POINTER(dev->ip6_ptr, NULL);
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 5cd94effbc92..15a37352124d 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -952,23 +952,22 @@ static void inet6_ifmcaddr_notify(struct net_device *dev,
 static int __ipv6_dev_mc_inc(struct net_device *dev,
 			     const struct in6_addr *addr, unsigned int mode)
 {
-	struct ifmcaddr6 *mc;
 	struct inet6_dev *idev;
-
-	ASSERT_RTNL();
+	struct ifmcaddr6 *mc;
 
 	/* we need to take a reference on idev */
 	idev = in6_dev_get(dev);
-
 	if (!idev)
 		return -EINVAL;
 
-	if (idev->dead) {
+	mutex_lock(&idev->mc_lock);
+
+	if (READ_ONCE(idev->dead)) {
+		mutex_unlock(&idev->mc_lock);
 		in6_dev_put(idev);
 		return -ENODEV;
 	}
 
-	mutex_lock(&idev->mc_lock);
 	for_each_mc_mclock(idev, mc) {
 		if (ipv6_addr_equal(&mc->mca_addr, addr)) {
 			mc->mca_users++;
-- 
2.49.0