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>

diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c
index da7c72105fb6e6cfd6bfe8a335f92befb43d5987..ca88119410852f7869cf32cbc31e47a3e17c21e6 100644 (file)
--- 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 bb07725d1c72b1332ec052af190a563456469c5f..c1d881dc6409a4dae9bd99562a4f11e93cce3d68 100644 (file)
--- 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 0d6d0d749d440e11714b7476d7138567039f16dc..07ebb800edf170e6fa662a44e26715fef2308930 100644 (file)
--- 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;
 

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 58df76fe408a4677db52a3c1f94674119dc4c925..ab5f201bf0ab41b463175f501e8560b4d64d9b0a 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3746,6 +3746,7 @@ static int rtnl_group_changelink(const struct sk_buff *skb,
 static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
                               const struct rtnl_link_ops *ops,
                               struct net *tgt_net, struct net *link_net,
+                              struct net *peer_net,
                               const struct nlmsghdr *nlh,
                               struct nlattr **tb, struct nlattr **data,
                               struct netlink_ext_ack *extack)
@@ -3776,8 +3777,13 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
 
        dev->ifindex = ifm->ifi_index;
 
+       if (link_net)
+               net = link_net;
+       if (peer_net)
+               net = peer_net;
+
        if (ops->newlink)
-               err = ops->newlink(link_net ? : net, dev, tb, data, extack);
+               err = ops->newlink(net, dev, tb, data, extack);
        else
                err = register_netdevice(dev);
        if (err < 0) {
@@ -3812,40 +3818,33 @@ out_unregister:
        goto out;
 }
 
-static int rtnl_add_peer_net(struct rtnl_nets *rtnl_nets,
-                            const struct rtnl_link_ops *ops,
-                            struct nlattr *data[],
-                            struct netlink_ext_ack *extack)
+static struct net *rtnl_get_peer_net(const struct rtnl_link_ops *ops,
+                                    struct nlattr *data[],
+                                    struct netlink_ext_ack *extack)
 {
        struct nlattr *tb[IFLA_MAX + 1];
-       struct net *net;
        int err;
 
        if (!data || !data[ops->peer_type])
-               return 0;
+               return NULL;
 
        err = rtnl_nla_parse_ifinfomsg(tb, data[ops->peer_type], extack);
        if (err < 0)
-               return err;
+               return ERR_PTR(err);
 
        if (ops->validate) {
                err = ops->validate(tb, NULL, extack);
                if (err < 0)
-                       return err;
+                       return ERR_PTR(err);
        }
 
-       net = rtnl_link_get_net_ifla(tb);
-       if (IS_ERR(net))
-               return PTR_ERR(net);
-       if (net)
-               rtnl_nets_add(rtnl_nets, net);
-
-       return 0;
+       return rtnl_link_get_net_ifla(tb);
 }
 
 static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
                          const struct rtnl_link_ops *ops,
                          struct net *tgt_net, struct net *link_net,
+                         struct net *peer_net,
                          struct rtnl_newlink_tbs *tbs,
                          struct nlattr **data,
                          struct netlink_ext_ack *extack)
@@ -3894,14 +3893,15 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
                return -EOPNOTSUPP;
        }
 
-       return rtnl_newlink_create(skb, ifm, ops, tgt_net, link_net, nlh, tb, data, extack);
+       return rtnl_newlink_create(skb, ifm, ops, tgt_net, link_net, peer_net, nlh,
+                                  tb, data, extack);
 }
 
 static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
                        struct netlink_ext_ack *extack)
 {
+       struct net *tgt_net, *link_net = NULL, *peer_net = NULL;
        struct nlattr **tb, **linkinfo, **data = NULL;
-       struct net *tgt_net, *link_net = NULL;
        struct rtnl_link_ops *ops = NULL;
        struct rtnl_newlink_tbs *tbs;
        struct rtnl_nets rtnl_nets;
@@ -3971,9 +3971,11 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
                }
 
                if (ops->peer_type) {
-                       ret = rtnl_add_peer_net(&rtnl_nets, ops, data, extack);
-                       if (ret < 0)
+                       peer_net = rtnl_get_peer_net(ops, data, extack);
+                       if (IS_ERR(peer_net))
                                goto put_ops;
+                       if (peer_net)
+                               rtnl_nets_add(&rtnl_nets, peer_net);
                }
        }
 
@@ -4004,7 +4006,7 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
        }
 
        rtnl_nets_lock(&rtnl_nets);
-       ret = __rtnl_newlink(skb, nlh, ops, tgt_net, link_net, tbs, data, extack);
+       ret = __rtnl_newlink(skb, nlh, ops, tgt_net, link_net, peer_net, tbs, data, extack);
        rtnl_nets_unlock(&rtnl_nets);
 
 put_net: