From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Xiao Liang <shaw.leon@gmail.com>,
	Maoyi Xie <maoyixie.tju@gmail.com>,
	Kuniyuki Iwashima <kuniyu@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 123/235] net: ip6_tunnel: require CAP_NET_ADMIN in the device netns for changelink
Date: Thu, 20 Aug 2026 16:55:59 +0200
Message-ID: <20260820145220.170095552@linuxfoundation.org>
In-Reply-To: <20260820145216.426568665@linuxfoundation.org>
References: <20260820145216.426568665@linuxfoundation.org>
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5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maoyi Xie <maoyixie.tju@gmail.com>

[ Upstream commit 2496fa0b7d180b3ad356b514e7ff93bb14e6140a ]

ip6_tnl_changelink() operates on at most two netns, dev_net(dev) and the
tunnel link netns t->net. They differ once the device is created in or
moved to a netns other than the one the request runs in. The rtnl
changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a
caller privileged there but not in t->net can rewrite a tunnel that
lives in t->net.

Gate ip6_tnl_changelink() on rtnl_dev_link_net_capable() at its top,
before any attribute is parsed.

Reported-by: Xiao Liang <shaw.leon@gmail.com>
Closes: https://lore.kernel.org/netdev/CABAhCOSzP1vaThGV35_VnsRCb=87_CPjPVsTHbq905k8A+BuUg@mail.gmail.com/
Fixes: 0bd8762824e7 ("ip6tnl: add x-netns support")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260612085941.3158249-5-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/ip6_tunnel.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -2083,6 +2083,9 @@ static int ip6_tnl_changelink(struct net
 	struct ip6_tnl_net *ip6n = net_generic(net, ip6_tnl_net_id);
 	struct ip_tunnel_encap ipencap;
 
+	if (!rtnl_dev_link_net_capable(dev, net))
+		return -EPERM;
+
 	if (dev == ip6n->fb_tnl_dev)
 		return -EINVAL;