[PATCH net-next V2 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 by allowing either qemu or libvirt to
attach eBPF filter to tun.

Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 drivers/net/tun.c           | 39 +++++++++++++++++++++++++++++++++++----
 include/uapi/linux/if_tun.h |  1 +
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 0853829..9fc8b70 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -238,6 +238,12 @@ 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;
 };
 
 static int tun_napi_receive(struct napi_struct *napi, int budget)
@@ -984,12 +990,25 @@ 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]);
@@ -1015,6 +1034,16 @@ 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);
+
+       /* Trim extra bytes since we may inster vlan proto & TCI
+        * in tun_put_user().
+        */
+       if (skb_vlan_tag_present(skb))
+               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;
 
@@ -1904,10 +1933,7 @@ 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));
@@ -2068,6 +2094,7 @@ 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 +2876,10 @@ 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