Commit 1d324c2f authored by Maoyi Xie's avatar Maoyi Xie Committed by Jakub Kicinski
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ip6_gre: Use cached t->net in ip6erspan_changelink(). 



After commit 5e72ce3e ("net: ipv6: Use link netns in newlink() of
rtnl_link_ops"), ip6erspan_newlink() correctly resolves the per-netns
ip6gre hash via link_net. ip6erspan_changelink() was not converted in
that series and still uses dev_net(dev), which diverges from the
device's creation netns after IFLA_NET_NS_FD migration.

This re-inserts the tunnel into the wrong per-netns hash. The
original netns keeps a stale entry. When that netns is later
destroyed, ip6gre_exit_rtnl_net() walks the stale entry, producing a
slab-use-after-free reported by KASAN, followed by a kernel BUG at
net/core/dev.c (LIST_POISON1) in unregister_netdevice_many_notify().

Reachable from an unprivileged user namespace (unshare --user
--map-root-user --net).

ip6gre_changelink() earlier in the same file already uses the cached
t->net; only ip6erspan_changelink() has the wrong shape.

Fixes: 2d665034 ("net: ip6_gre: Fix ip6erspan hlen calculation")
Cc: stable@vger.kernel.org # v5.15+
Signed-off-by: default avatarMaoyi Xie <maoyi.xie@ntu.edu.sg>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260430103318.3206018-1-maoyi.xie@ntu.edu.sg


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 386829cd

net/ipv6/ip6_gre.c

+3 −2
Original line number Diff line number Diff line
@@ -2262,10 +2262,11 @@ static int ip6erspan_changelink(struct net_device *dev, struct nlattr *tb[], 
				struct nlattr *data[],

				struct netlink_ext_ack *extack)

{

	struct ip6gre_net *ign = net_generic(dev_net(dev), ip6gre_net_id);

	struct ip6_tnl *t = netdev_priv(dev);

	struct __ip6_tnl_parm p;

	struct ip6_tnl *t;

	struct ip6gre_net *ign;



	ign = net_generic(t->net, ip6gre_net_id);

	t = ip6gre_changelink_common(dev, tb, data, &p, extack);

	if (IS_ERR(t))

		return PTR_ERR(t);