FAILED: patch "[PATCH] net: ip_gre: require CAP_NET_ADMIN in the device netns for" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 8165f7ff57d9667d2bb477ef6af83ede7fed4ad7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026070222-bullhorn-skilled-e133@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8165f7ff57d9667d2bb477ef6af83ede7fed4ad7 Mon Sep 17 00:00:00 2001
From: Maoyi Xie <maoyixie.tju@gmail.com>
Date: Fri, 12 Jun 2026 16:59:35 +0800
Subject: [PATCH] net: ip_gre: require CAP_NET_ADMIN in the device netns for
 changelink

A tunnel 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.

Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in
net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is
skipped when the link netns is dev_net(dev), where the rtnl path already
checked it. The other patches in this series use the same helper.

Gate ipgre_changelink() and erspan_changelink() with it, at the top of
the op before any attribute is parsed, because the parsers update live
tunnel fields first. ipgre_netlink_parms() sets t->collect_md before
ip_tunnel_changelink() runs.

Commit 8b484efd5cb4 ("ip6: vti: Use ip6_tnl.net in
vti6_siocdevprivate().") added the same check on the ioctl path. This
adds it on RTM_NEWLINK.

Reported-by: Xiao Liang <shaw.leon@gmail.com>
Closes: https://lore.kernel.org/netdev/CABAhCOSzP1vaThGV35_VnsRCb=87_CPjPVsTHbq905k8A+BuUg@mail.gmail.com/
Fixes: b57708add314 ("gre: 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/20260612085941.3158249-2-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index ec65a8cebb99..2bff41aacc98 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -256,6 +256,8 @@ int rtnl_configure_link(struct net_device *dev, const struct ifinfomsg *ifm,
 int rtnl_nla_parse_ifinfomsg(struct nlattr **tb, const struct nlattr *nla_peer,
 			     struct netlink_ext_ack *exterr);
 struct net *rtnl_get_net_ns_capable(struct sock *sk, int netnsid);
+bool rtnl_dev_link_net_capable(const struct net_device *dev,
+			       const struct net *link_net);
 
 #define MODULE_ALIAS_RTNL_LINK(kind) MODULE_ALIAS("rtnl-link-" kind)
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 61d095ce1b3b..12aa3aa1688b 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2438,6 +2438,14 @@ struct net *rtnl_get_net_ns_capable(struct sock *sk, int netnsid)
 }
 EXPORT_SYMBOL_GPL(rtnl_get_net_ns_capable);
 
+bool rtnl_dev_link_net_capable(const struct net_device *dev,
+			       const struct net *link_net)
+{
+	return net_eq(link_net, dev_net(dev)) ||
+	       ns_capable(link_net->user_ns, CAP_NET_ADMIN);
+}
+EXPORT_SYMBOL_GPL(rtnl_dev_link_net_capable);
+
 static int rtnl_valid_dump_ifinfo_req(const struct nlmsghdr *nlh,
 				      bool strict_check, struct nlattr **tb,
 				      struct netlink_ext_ack *extack)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 208dd48012d9..3efdfb4ffa21 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1457,6 +1457,9 @@ static int ipgre_changelink(struct net_device *dev, struct nlattr *tb[],
 	__u32 fwmark = t->fwmark;
 	int err;
 
+	if (!rtnl_dev_link_net_capable(dev, t->net))
+		return -EPERM;
+
 	err = ipgre_newlink_encap_setup(dev, data);
 	if (err)
 		return err;
@@ -1486,6 +1489,9 @@ static int erspan_changelink(struct net_device *dev, struct nlattr *tb[],
 	__u32 fwmark = t->fwmark;
 	int err;
 
+	if (!rtnl_dev_link_net_capable(dev, t->net))
+		return -EPERM;
+
 	err = ipgre_newlink_encap_setup(dev, data);
 	if (err)
 		return err;