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ip6_gre: Use cached t->net in ip6erspan_changelink().

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After commit 5e72ce3e39 ("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: 2d665034f2 ("net: ip6_gre: Fix ip6erspan hlen calculation")
Cc: stable@vger.kernel.org # v5.15+
Signed-off-by: Maoyi Xie <maoyi.xie@ntu.edu.sg>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260430103318.3206018-1-maoyi.xie@ntu.edu.sg
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Maoyi Xie
2026-05-02 10:36:21 -07:00
committed by Jakub Kicinski
parent 386829cd89
commit 1d324c2f43
1 changed files with 3 additions and 2 deletions
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net/ipv6/ip6_gre.c
+3 -2
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@@ -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);