[PATCH net-next 2/2] tun: allow to attach ebpf socket filter

[Jason Wang]

This patch allows userspace to attach eBPF filter to tun. This will
allow to implement VM dataplane filtering in a more efficient way
compared to cBPF filter.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/tun.c           | 26 ++++++++++++++++++++++++++
 include/uapi/linux/if_tun.h |  1 +
 2 files changed, 27 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 0853829..6e9452b 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -238,6 +238,7 @@ struct tun_struct {
 	struct tun_pcpu_stats __percpu *pcpu_stats;
 	struct bpf_prog __rcu *xdp_prog;
 	struct tun_prog __rcu *steering_prog;
+	struct tun_prog __rcu *filter_prog;
 };
 
 static int tun_napi_receive(struct napi_struct *napi, int budget)
@@ -984,12 +985,25 @@ static void tun_automq_xmit(struct tun_struct *tun, struct sk_buff *skb)
 #endif
 }
 
+static unsigned int run_ebpf_filter(struct tun_struct *tun,
+				    struct sk_buff *skb,
+				    int len)
+{
+	struct tun_prog *prog = rcu_dereference(tun->filter_prog);
+
+	if (prog)
+		len = bpf_prog_run_clear_cb(prog->prog, skb);
+
+	return len;
+}
+
 /* Net device start xmit */
 static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
 	int txq = skb->queue_mapping;
 	struct tun_file *tfile;
+	int len = skb->len;
 
 	rcu_read_lock();
 	tfile = rcu_dereference(tun->tfiles[txq]);
@@ -1015,9 +1029,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	    sk_filter(tfile->socket.sk, skb))
 		goto drop;
 
+	len = run_ebpf_filter(tun, skb, len);
+	if (!len)
+		goto drop;
+
 	if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
 		goto drop;
 
+	if (pskb_trim(skb, len))
+		goto drop;
+
 	skb_tx_timestamp(skb);
 
 	/* Orphan the skb - required as we might hang on to it
@@ -2068,6 +2089,7 @@ static void tun_free_netdev(struct net_device *dev)
 	tun_flow_uninit(tun);
 	security_tun_dev_free_security(tun->security);
 	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
+	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
 }
 
 static void tun_setup(struct net_device *dev)
@@ -2849,6 +2871,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = tun_set_ebpf(tun, &tun->steering_prog, argp);
 		break;
 
+	case TUNSETFILTEREBPF:
+		ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index fb38c17..ee432cd 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -58,6 +58,7 @@
 #define TUNSETVNETBE _IOW('T', 222, int)
 #define TUNGETVNETBE _IOR('T', 223, int)
 #define TUNSETSTEERINGEBPF _IOR('T', 224, int)
+#define TUNSETFILTEREBPF _IOR('T', 225, int)
 
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001
-- 
2.7.4