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net: netlink: virtual tap device management 

Similarly to the networking receive path with ptype_all taps, we add
the possibility to register netdevices that are for ARPHRD_NETLINK to
the netlink subsystem, so that those can be used for netlink analyzers
resp. debuggers. We do not offer a direct callback function as out-of-tree
modules could do crap with it. Instead, a netdevice must be registered
properly and only receives a clone, managed by the netlink layer. Symbols
are exported as GPL-only.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2013-06-21 19:38:07 +02:00 committed by David S. Miller
parent 77e2af0312
commit bcbde0d449
2 changed files with 117 additions and 0 deletions
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10
include/linux/netlink.h
View File

@ -145,4 +145,14 @@ static inline int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
return __netlink_dump_start(ssk, skb, nlh, control);
}
struct netlink_tap {
struct net_device *dev;
struct module *module;
struct list_head list;
};
extern int netlink_add_tap(struct netlink_tap *nt);
extern int __netlink_remove_tap(struct netlink_tap *nt);
extern int netlink_remove_tap(struct netlink_tap *nt);
#endif /* __LINUX_NETLINK_H */

107
net/netlink/af_netlink.c
View File

@ -57,6 +57,7 @@
#include <linux/audit.h>
#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/if_arp.h>
#include <asm/cacheflush.h>
#include <net/net_namespace.h>
@ -101,6 +102,9 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
static ATOMIC_NOTIFIER_HEAD(netlink_chain);
static DEFINE_SPINLOCK(netlink_tap_lock);
static struct list_head netlink_tap_all __read_mostly;
static inline u32 netlink_group_mask(u32 group)
{
return group ? 1 << (group - 1) : 0;
@ -111,6 +115,100 @@ static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u
return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
}
int netlink_add_tap(struct netlink_tap *nt)
{
if (unlikely(nt->dev->type != ARPHRD_NETLINK))
return -EINVAL;
spin_lock(&netlink_tap_lock);
list_add_rcu(&nt->list, &netlink_tap_all);
spin_unlock(&netlink_tap_lock);
if (nt->module)
__module_get(nt->module);
return 0;
}
EXPORT_SYMBOL_GPL(netlink_add_tap);
int __netlink_remove_tap(struct netlink_tap *nt)
{
bool found = false;
struct netlink_tap *tmp;
spin_lock(&netlink_tap_lock);
list_for_each_entry(tmp, &netlink_tap_all, list) {
if (nt == tmp) {
list_del_rcu(&nt->list);
found = true;
goto out;
}
}
pr_warn("__netlink_remove_tap: %p not found\n", nt);
out:
spin_unlock(&netlink_tap_lock);
if (found && nt->module)
module_put(nt->module);
return found ? 0 : -ENODEV;
}
EXPORT_SYMBOL_GPL(__netlink_remove_tap);
int netlink_remove_tap(struct netlink_tap *nt)
{
int ret;
ret = __netlink_remove_tap(nt);
synchronize_net();
return ret;
}
EXPORT_SYMBOL_GPL(netlink_remove_tap);
static int __netlink_deliver_tap_skb(struct sk_buff *skb,
struct net_device *dev)
{
struct sk_buff *nskb;
int ret = -ENOMEM;
dev_hold(dev);
nskb = skb_clone(skb, GFP_ATOMIC);
if (nskb) {
nskb->dev = dev;
ret = dev_queue_xmit(nskb);
if (unlikely(ret > 0))
ret = net_xmit_errno(ret);
}
dev_put(dev);
return ret;
}
static void __netlink_deliver_tap(struct sk_buff *skb)
{
int ret;
struct netlink_tap *tmp;
list_for_each_entry_rcu(tmp, &netlink_tap_all, list) {
ret = __netlink_deliver_tap_skb(skb, tmp->dev);
if (unlikely(ret))
break;
}
}
static void netlink_deliver_tap(struct sk_buff *skb)
{
rcu_read_lock();
if (unlikely(!list_empty(&netlink_tap_all)))
__netlink_deliver_tap(skb);
rcu_read_unlock();
}
static void netlink_overrun(struct sock *sk)
{
struct netlink_sock *nlk = nlk_sk(sk);
@ -1518,6 +1616,8 @@ static int __netlink_sendskb(struct sock *sk, struct sk_buff *skb)
{
int len = skb->len;
netlink_deliver_tap(skb);
#ifdef CONFIG_NETLINK_MMAP
if (netlink_skb_is_mmaped(skb))
netlink_queue_mmaped_skb(sk, skb);
@ -1578,6 +1678,11 @@ static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb,
ret = -ECONNREFUSED;
if (nlk->netlink_rcv != NULL) {
/* We could do a netlink_deliver_tap(skb) here as well
* but since this is intended for the kernel only, we
* should rather let it stay under the hood.
*/
ret = skb->len;
netlink_skb_set_owner_r(skb, sk);
NETLINK_CB(skb).sk = ssk;
@ -2975,6 +3080,8 @@ static int __init netlink_proto_init(void)
nl_table[i].compare = netlink_compare;
}
INIT_LIST_HEAD(&netlink_tap_all);
netlink_add_usersock_entry();
sock_register(&netlink_family_ops);