rtnetlink: fix double call of rtnl_link_get_net_ifla()

Currently rtnl_link_get_net_ifla() gets called twice when we create
peer devices, once in rtnl_add_peer_net() and once in each ->newlink()
implementation.

This looks safer, however, it leads to a classic Time-of-Check to
Time-of-Use (TOCTOU) bug since IFLA_NET_NS_PID is very dynamic. And
because of the lack of checking error pointer of the second call, it
also leads to a kernel crash as reported by syzbot.

Fix this by getting rid of the second call, which already becomes
redudant after Kuniyuki's work. We have to propagate the result of the
first rtnl_link_get_net_ifla() down to each ->newlink().

Reported-by: syzbot+21ba4d5adff0b6a7cfc6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=21ba4d5adff0b6a7cfc6
Fixes: 0eb87b02a705 ("veth: Set VETH_INFO_PEER to veth_link_ops.peer_type.")
Fixes: 6b84e558e95d ("vxcan: Set VXCAN_INFO_PEER to vxcan_link_ops.peer_type.")
Fixes: fefd5d082172 ("netkit: Set IFLA_NETKIT_PEER_INFO to netkit_link_ops.peer_type.")
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241129212519.825567-1-xiyou.wangcong@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 8 insertions, 25 deletions

diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c
index da7c72105fb6..ca8811941085 100644
--- a/drivers/net/can/vxcan.c
+++ b/drivers/net/can/vxcan.c
@@ -172,13 +172,12 @@ static void vxcan_setup(struct net_device *dev)
 /* forward declaration for rtnl_create_link() */
 static struct rtnl_link_ops vxcan_link_ops;
 
-static int vxcan_newlink(struct net *net, struct net_device *dev,
+static int vxcan_newlink(struct net *peer_net, struct net_device *dev,
 			 struct nlattr *tb[], struct nlattr *data[],
 			 struct netlink_ext_ack *extack)
 {
 	struct vxcan_priv *priv;
 	struct net_device *peer;
-	struct net *peer_net;
 
 	struct nlattr *peer_tb[IFLA_MAX + 1], **tbp = tb;
 	char ifname[IFNAMSIZ];
@@ -203,20 +202,15 @@ static int vxcan_newlink(struct net *net, struct net_device *dev,
 		name_assign_type = NET_NAME_ENUM;
 	}
 
-	peer_net = rtnl_link_get_net(net, tbp);
 	peer = rtnl_create_link(peer_net, ifname, name_assign_type,
 				&vxcan_link_ops, tbp, extack);
-	if (IS_ERR(peer)) {
-		put_net(peer_net);
+	if (IS_ERR(peer))
 		return PTR_ERR(peer);
-	}
 
 	if (ifmp && dev->ifindex)
 		peer->ifindex = ifmp->ifi_index;
 
 	err = register_netdevice(peer);
-	put_net(peer_net);
-	peer_net = NULL;
 	if (err < 0) {
 		free_netdev(peer);
 		return err;
diff --git a/drivers/net/netkit.c b/drivers/net/netkit.c
index bb07725d1c72..c1d881dc6409 100644
--- a/drivers/net/netkit.c
+++ b/drivers/net/netkit.c
@@ -327,7 +327,7 @@ static int netkit_validate(struct nlattr *tb[], struct nlattr *data[],
 
 static struct rtnl_link_ops netkit_link_ops;
 
-static int netkit_new_link(struct net *src_net, struct net_device *dev,
+static int netkit_new_link(struct net *peer_net, struct net_device *dev,
 			   struct nlattr *tb[], struct nlattr *data[],
 			   struct netlink_ext_ack *extack)
 {
@@ -342,7 +342,6 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 	struct net_device *peer;
 	char ifname[IFNAMSIZ];
 	struct netkit *nk;
-	struct net *net;
 	int err;
 
 	if (data) {
@@ -385,13 +384,10 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 	    (tb[IFLA_ADDRESS] || tbp[IFLA_ADDRESS]))
 		return -EOPNOTSUPP;
 
-	net = rtnl_link_get_net(src_net, tbp);
-	peer = rtnl_create_link(net, ifname, ifname_assign_type,
+	peer = rtnl_create_link(peer_net, ifname, ifname_assign_type,
 				&netkit_link_ops, tbp, extack);
-	if (IS_ERR(peer)) {
-		put_net(net);
+	if (IS_ERR(peer))
 		return PTR_ERR(peer);
-	}
 
 	netif_inherit_tso_max(peer, dev);
 
@@ -408,7 +404,6 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 	bpf_mprog_bundle_init(&nk->bundle);
 
 	err = register_netdevice(peer);
-	put_net(net);
 	if (err < 0)
 		goto err_register_peer;
 	netif_carrier_off(peer);
diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 0d6d0d749d44..07ebb800edf1 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1765,7 +1765,7 @@ static int veth_init_queues(struct net_device *dev, struct nlattr *tb[])
 	return 0;
 }
 
-static int veth_newlink(struct net *src_net, struct net_device *dev,
+static int veth_newlink(struct net *peer_net, struct net_device *dev,
 			struct nlattr *tb[], struct nlattr *data[],
 			struct netlink_ext_ack *extack)
 {
@@ -1776,7 +1776,6 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 	struct nlattr *peer_tb[IFLA_MAX + 1], **tbp;
 	unsigned char name_assign_type;
 	struct ifinfomsg *ifmp;
-	struct net *net;
 
 	/*
 	 * create and register peer first
@@ -1800,13 +1799,10 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 		name_assign_type = NET_NAME_ENUM;
 	}
 
-	net = rtnl_link_get_net(src_net, tbp);
-	peer = rtnl_create_link(net, ifname, name_assign_type,
+	peer = rtnl_create_link(peer_net, ifname, name_assign_type,
 				&veth_link_ops, tbp, extack);
-	if (IS_ERR(peer)) {
-		put_net(net);
+	if (IS_ERR(peer))
 		return PTR_ERR(peer);
-	}
 
 	if (!ifmp || !tbp[IFLA_ADDRESS])
 		eth_hw_addr_random(peer);
@@ -1817,8 +1813,6 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 	netif_inherit_tso_max(peer, dev);
 
 	err = register_netdevice(peer);
-	put_net(net);
-	net = NULL;
 	if (err < 0)
 		goto err_register_peer;