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loopback: create blackhole net device similar to loopack. 

Create a blackhole net device that can be used for "dead"
dst entries instead of loopback device. This blackhole device differs
from loopback in few aspects: (a) It's not per-ns. (b)  MTU on this
device is ETH_MIN_MTU (c) The xmit function is essentially kfree_skb().
and (d) since it's not registered it won't have ifindex.

Lower MTU effectively make the device not pass the MTU check during
the route check when a dst associated with the skb is dead.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Mahesh Bandewar 2019-07-01 14:38:49 -07:00 committed by David S. Miller
parent 8909783cb5
commit 4de83b88c6
2 changed files with 69 additions and 9 deletions
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76
drivers/net/loopback.c
View File

@ -55,6 +55,13 @@
#include <net/net_namespace.h> #include <net/net_namespace.h>
#include <linux/u64_stats_sync.h> #include <linux/u64_stats_sync.h>
/* blackhole_netdev - a device used for dsts that are marked expired!
* This is global device (instead of per-net-ns) since it's not needed
* to be per-ns and gets initialized at boot time.
*/
struct net_device *blackhole_netdev;
EXPORT_SYMBOL(blackhole_netdev);
/* The higher levels take care of making this non-reentrant (it's /* The higher levels take care of making this non-reentrant (it's
* called with bh's disabled). * called with bh's disabled).
*/ */
@ -150,12 +157,14 @@ static const struct net_device_ops loopback_ops = {
.ndo_set_mac_address = eth_mac_addr, .ndo_set_mac_address = eth_mac_addr,
}; };
/* The loopback device is special. There is only one instance static void gen_lo_setup(struct net_device *dev,
* per network namespace. unsigned int mtu,
*/ const struct ethtool_ops *eth_ops,
static void loopback_setup(struct net_device *dev) const struct header_ops *hdr_ops,
const struct net_device_ops *dev_ops,
void (*dev_destructor)(struct net_device *dev))
{ {
dev->mtu = 64 * 1024; dev->mtu = mtu;
dev->hard_header_len = ETH_HLEN; /* 14 */ dev->hard_header_len = ETH_HLEN; /* 14 */
dev->min_header_len = ETH_HLEN; /* 14 */ dev->min_header_len = ETH_HLEN; /* 14 */
dev->addr_len = ETH_ALEN; /* 6 */ dev->addr_len = ETH_ALEN; /* 6 */
@ -174,11 +183,20 @@ static void loopback_setup(struct net_device *dev)
| NETIF_F_NETNS_LOCAL | NETIF_F_NETNS_LOCAL
| NETIF_F_VLAN_CHALLENGED | NETIF_F_VLAN_CHALLENGED
| NETIF_F_LOOPBACK; | NETIF_F_LOOPBACK;
dev->ethtool_ops = &loopback_ethtool_ops; dev->ethtool_ops = eth_ops;
dev->header_ops = &eth_header_ops; dev->header_ops = hdr_ops;
dev->netdev_ops = &loopback_ops; dev->netdev_ops = dev_ops;
dev->needs_free_netdev = true; dev->needs_free_netdev = true;
dev->priv_destructor = loopback_dev_free; dev->priv_destructor = dev_destructor;
}
/* The loopback device is special. There is only one instance
* per network namespace.
*/
static void loopback_setup(struct net_device *dev)
{
gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
&loopback_ops, loopback_dev_free);
} }
/* Setup and register the loopback device. */ /* Setup and register the loopback device. */
@ -213,3 +231,43 @@ out:
struct pernet_operations __net_initdata loopback_net_ops = { struct pernet_operations __net_initdata loopback_net_ops = {
.init = loopback_net_init, .init = loopback_net_init,
}; };
/* blackhole netdevice */
static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
struct net_device *dev)
{
kfree_skb(skb);
net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
return NETDEV_TX_OK;
}
static const struct net_device_ops blackhole_netdev_ops = {
.ndo_start_xmit = blackhole_netdev_xmit,
};
/* This is a dst-dummy device used specifically for invalidated
* DSTs and unlike loopback, this is not per-ns.
*/
static void blackhole_netdev_setup(struct net_device *dev)
{
gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
}
/* Setup and register the blackhole_netdev. */
static int __init blackhole_netdev_init(void)
{
blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
blackhole_netdev_setup);
if (!blackhole_netdev)
return -ENOMEM;
dev_init_scheduler(blackhole_netdev);
dev_activate(blackhole_netdev);
blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
dev_net_set(blackhole_netdev, &init_net);
return 0;
}
device_initcall(blackhole_netdev_init);

2
include/linux/netdevice.h
View File

@ -4870,4 +4870,6 @@ do { \
#define PTYPE_HASH_SIZE (16) #define PTYPE_HASH_SIZE (16)
#define PTYPE_HASH_MASK (PTYPE_HASH_SIZE - 1) #define PTYPE_HASH_MASK (PTYPE_HASH_SIZE - 1)
extern struct net_device *blackhole_netdev;
#endif /* _LINUX_NETDEVICE_H */ #endif /* _LINUX_NETDEVICE_H */