Commit cbaaa632 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Jakub Kicinski
Browse files

rtnetlink: Introduce struct rtnl_nets and helpers. 



rtnl_newlink() needs to hold 3 per-netns RTNL: 2 for a new device
and 1 for its peer.

We will add rtnl_nets_lock() later, which performs the nested locking
based on struct rtnl_nets, which has an array of struct net pointers.

rtnl_nets_add() adds a net pointer to the array and sorts it so that
rtnl_nets_lock() can simply acquire per-netns RTNL from array[0] to [2].

Before calling rtnl_nets_add(), get_net() must be called for the net,
and rtnl_nets_destroy() will call put_net() for each.

Let's apply the helpers to rtnl_newlink().

When CONFIG_DEBUG_NET_SMALL_RTNL is disabled, we do not call
rtnl_net_lock() thus do not care about the array order, so
rtnl_net_cmp_locks() returns -1 so that the loop in rtnl_nets_add()
can be optimised to NOP.

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarNikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20241108004823.29419-5-kuniyu@amazon.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 68297dbb

net/core/rtnetlink.c

+67 −3
Original line number Diff line number Diff line
@@ -258,8 +258,67 @@ bool lockdep_rtnl_net_is_held(struct net *net) 
	return lockdep_rtnl_is_held() && lockdep_is_held(&net->rtnl_mutex);

}

EXPORT_SYMBOL(lockdep_rtnl_net_is_held);

#else

static int rtnl_net_cmp_locks(const struct net *net_a, const struct net *net_b)

{

	/* No need to swap */

	return -1;

}

#endif



struct rtnl_nets {

	/* ->newlink() needs to freeze 3 netns at most;

	 * 2 for the new device, 1 for its peer.

	 */

	struct net *net[3];

	unsigned char len;

};



static void rtnl_nets_init(struct rtnl_nets *rtnl_nets)

{

	memset(rtnl_nets, 0, sizeof(*rtnl_nets));

}



static void rtnl_nets_destroy(struct rtnl_nets *rtnl_nets)

{

	int i;



	for (i = 0; i < rtnl_nets->len; i++) {

		put_net(rtnl_nets->net[i]);

		rtnl_nets->net[i] = NULL;

	}



	rtnl_nets->len = 0;

}



/**

 * rtnl_nets_add - Add netns to be locked before ->newlink().

 *

 * @rtnl_nets: rtnl_nets pointer passed to ->get_peer_net().

 * @net: netns pointer with an extra refcnt held.

 *

 * The extra refcnt is released in rtnl_nets_destroy().

 */

static void rtnl_nets_add(struct rtnl_nets *rtnl_nets, struct net *net)

{

	int i;



	DEBUG_NET_WARN_ON_ONCE(rtnl_nets->len == ARRAY_SIZE(rtnl_nets->net));



	for (i = 0; i < rtnl_nets->len; i++) {

		switch (rtnl_net_cmp_locks(rtnl_nets->net[i], net)) {

		case 0:

			put_net(net);

			return;

		case 1:

			swap(rtnl_nets->net[i], net);

		}

	}



	rtnl_nets->net[i] = net;

	rtnl_nets->len++;

}



static struct rtnl_link __rcu *__rcu *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];



static inline int rtm_msgindex(int msgtype)
@@ -3767,6 +3826,7 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, 
	struct net *tgt_net, *link_net = NULL;

	struct rtnl_link_ops *ops = NULL;

	struct rtnl_newlink_tbs *tbs;

	struct rtnl_nets rtnl_nets;

	int ops_srcu_index;

	int ret;
@@ -3810,6 +3870,8 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, 
#endif

	}



	rtnl_nets_init(&rtnl_nets);



	if (ops) {

		if (ops->maxtype > RTNL_MAX_TYPE) {

			ret = -EINVAL;
@@ -3839,6 +3901,8 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, 
		goto put_ops;

	}



	rtnl_nets_add(&rtnl_nets, tgt_net);



	if (tb[IFLA_LINK_NETNSID]) {

		int id = nla_get_s32(tb[IFLA_LINK_NETNSID]);
@@ -3849,6 +3913,8 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, 
			goto put_net;

		}



		rtnl_nets_add(&rtnl_nets, link_net);



		if (!netlink_ns_capable(skb, link_net->user_ns, CAP_NET_ADMIN)) {

			ret = -EPERM;

			goto put_net;
@@ -3858,9 +3924,7 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, 
	ret = __rtnl_newlink(skb, nlh, ops, tgt_net, link_net, tbs, data, extack);



put_net:

	if (link_net)

		put_net(link_net);

	put_net(tgt_net);

	rtnl_nets_destroy(&rtnl_nets);

put_ops:

	if (ops)

		rtnl_link_ops_put(ops, ops_srcu_index);