On Wed, May 04, 2022 at 04:06:10PM +0200, Johannes Nixdorf wrote:

commit 9995b408f17ff8c7f11bc725c8aa225ba3a63b1c upstream.

There are two reasons for addrconf_notify() to be called with NETDEV_DOWN: either the network device is actually going down, or IPv6 was disabled on the interface.

If either of them stays down while the other is toggled, we repeatedly call the code for NETDEV_DOWN, including ipv6_mc_down(), while never calling the corresponding ipv6_mc_up() in between. This will cause a new entry in idev->mc_tomb to be allocated for each multicast group the interface is subscribed to, which in turn leaks one struct ifmcaddr6 per nontrivial multicast group the interface is subscribed to.

The following reproducer will leak at least $n objects:

ip addr add ff2e::4242/32 dev eth0 autojoin sysctl -w net.ipv6.conf.eth0.disable_ipv6=1 for i in $(seq 1 $n); do ip link set up eth0; ip link set down eth0 done

Joining groups with IPV6_ADD_MEMBERSHIP (unprivileged) or setting the sysctl net.ipv6.conf.eth0.forwarding to 1 (=> subscribing to ff02::2) can also be used to create a nontrivial idev->mc_list, which will the leak objects with the right up-down-sequence.

Based on both sources for NETDEV_DOWN events the interface IPv6 state should be considered:

• not ready if the network interface is not ready OR IPv6 is disabled for it
• ready if the network interface is ready AND IPv6 is enabled for it

The functions ipv6_mc_up() and ipv6_down() should only be run when this state changes.

Implement this by remembering when the IPv6 state is ready, and only run ipv6_mc_down() if it actually changed from ready to not ready.

The other direction (not ready -> ready) already works correctly, as:

• the interface notification triggered codepath for NETDEV_UP / NETDEV_CHANGE returns early if ipv6 is disabled, and
• the disable_ipv6=0 triggered codepath skips fully initializing the interface as long as addrconf_link_ready(dev) returns false
• calling ipv6_mc_up() repeatedly does not leak anything

Fixes: 3ce62a84d53c ("ipv6: exit early in addrconf_notify() if IPv6 is disabled") Signed-off-by: Johannes Nixdorf j.nixdorf@avm.de Signed-off-by: David S. Miller davem@davemloft.net [jnixdorf: context updated for bpo to v4.19/v5.4] Signed-off-by: Johannes Nixdorf j.nixdorf@avm.de

---

net/ipv6/addrconf.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 9d8b791f63ef..295adfabf870 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -3660,6 +3660,7 @@ static int addrconf_ifdown(struct net_device *dev, int how) struct inet6_dev *idev; struct inet6_ifaddr *ifa, *tmp; bool keep_addr = false;

• bool was_ready; int state, i;

ASSERT_RTNL(); @@ -3725,7 +3726,10 @@ static int addrconf_ifdown(struct net_device *dev, int how) addrconf_del_rs_timer(idev);

• /* Step 2: clear flags for stateless addrconf */

• /* Step 2: clear flags for stateless addrconf, repeated down

• *         detection
  

• */
  

• was_ready = idev->if_flags & IF_READY; if (!how) idev->if_flags &= ~(IF_RS_SENT|IF_RA_RCVD|IF_READY);

@@ -3799,7 +3803,7 @@ static int addrconf_ifdown(struct net_device *dev, int how) if (how) { ipv6_ac_destroy_dev(idev); ipv6_mc_destroy_dev(idev);

• } else {

• } else if (was_ready) { ipv6_mc_down(idev); }

2.36.0

All now queued up, thanks.

greg k-h