tun: allow to attach ebpf socket filter

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 by allowing either qemu or libvirt to
attach eBPF filter to tun.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 35 insertions, 4 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 76197ede22a9..170a3e89b5af 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -239,6 +239,12 @@ 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;
+};
+
+struct veth {
+        __be16 h_vlan_proto;
+        __be16 h_vlan_TCI;
 };
 
 bool tun_is_xdp_buff(void *ptr)
@@ -1036,12 +1042,25 @@ 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]);
@@ -1067,6 +1086,15 @@ 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);
+
+        /* Trim extra bytes since we may insert vlan proto & TCI
+         * in tun_put_user().
+         */
+        len -= skb_vlan_tag_present(skb) ? sizeof(struct veth) : 0;
+        if (len <= 0 || pskb_trim(skb, len))
+                goto drop;
+
         if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
                 goto drop;
 
@@ -2054,10 +2082,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
 
         if (vlan_hlen) {
                 int ret;
-                struct {
-                        __be16 h_vlan_proto;
-                        __be16 h_vlan_TCI;
-                } veth;
+                struct veth veth;
 
                 veth.h_vlan_proto = skb->vlan_proto;
                 veth.h_vlan_TCI = htons(skb_vlan_tag_get(skb));
@@ -2225,6 +2250,7 @@ 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)
@@ -3019,6 +3045,10 @@ 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 fb38c1797131..ee432cd3018c 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