From: Maoyi Xie <maoyixie.tju@gmail.com>
Date: Thu, 30 Apr 2026 10:33:18 +0000 (+0800)
Subject: ip6_gre: Use cached t->net in ip6erspan_changelink().
X-Git-Tag: v7.1-rc3~26^2~49
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1d324c2f43f70c965f25c58cc3611c779adbe47e;p=thirdparty%2Fkernel%2Flinux.git

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

After commit 5e72ce3e3980 ("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: 2d665034f239 ("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>
---

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 63fc8556b475..365b4059eb20 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -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);