packet: add classic BPF fanout mode

Add fanout mode PACKET_FANOUT_CBPF that accepts a classic BPF program
to select a socket.

This avoids having to keep adding special case fanout modes. One
example use case is application layer load balancing. The QUIC
protocol, for instance, encodes a connection ID in UDP payload.

Also add socket option SOL_PACKET/PACKET_FANOUT_DATA that updates data
associated with the socket group. Fanout mode PACKET_FANOUT_CBPF is the
only user so far.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 104 insertions, 2 deletions

diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
index d3d715f8c88f..a4bb16fa822e 100644
--- a/include/uapi/linux/if_packet.h
+++ b/include/uapi/linux/if_packet.h
@@ -55,6 +55,7 @@ struct sockaddr_ll {
 #define PACKET_TX_HAS_OFF               19
 #define PACKET_QDISC_BYPASS             20
 #define PACKET_ROLLOVER_STATS           21
+#define PACKET_FANOUT_DATA              22
 
 #define PACKET_FANOUT_HASH              0
 #define PACKET_FANOUT_LB                1
@@ -62,6 +63,7 @@ struct sockaddr_ll {
 #define PACKET_FANOUT_ROLLOVER          3
 #define PACKET_FANOUT_RND               4
 #define PACKET_FANOUT_QM                5
+#define PACKET_FANOUT_CBPF              6
 #define PACKET_FANOUT_FLAG_ROLLOVER     0x1000
 #define PACKET_FANOUT_FLAG_DEFRAG       0x8000
 
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index b5afe538bb88..8869d07013e6 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -92,6 +92,7 @@
 #ifdef CONFIG_INET
 #include <net/inet_common.h>
 #endif
+#include <linux/bpf.h>
 
 #include "internal.h"
 
@@ -1410,6 +1411,22 @@ static unsigned int fanout_demux_qm(struct packet_fanout *f,
         return skb_get_queue_mapping(skb) % num;
 }
 
+static unsigned int fanout_demux_bpf(struct packet_fanout *f,
+                                     struct sk_buff *skb,
+                                     unsigned int num)
+{
+        struct bpf_prog *prog;
+        unsigned int ret = 0;
+
+        rcu_read_lock();
+        prog = rcu_dereference(f->bpf_prog);
+        if (prog)
+                ret = BPF_PROG_RUN(prog, skb) % num;
+        rcu_read_unlock();
+
+        return ret;
+}
+
 static bool fanout_has_flag(struct packet_fanout *f, u16 flag)
 {
         return f->flags & (flag >> 8);
@@ -1454,6 +1471,9 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev,
         case PACKET_FANOUT_ROLLOVER:
                 idx = fanout_demux_rollover(f, skb, 0, false, num);
                 break;
+        case PACKET_FANOUT_CBPF:
+                idx = fanout_demux_bpf(f, skb, num);
+                break;
         }
 
         if (fanout_has_flag(f, PACKET_FANOUT_FLAG_ROLLOVER))
@@ -1502,6 +1522,74 @@ static bool match_fanout_group(struct packet_type *ptype, struct sock *sk)
         return false;
 }
 
+static void fanout_init_data(struct packet_fanout *f)
+{
+        switch (f->type) {
+        case PACKET_FANOUT_LB:
+                atomic_set(&f->rr_cur, 0);
+                break;
+        case PACKET_FANOUT_CBPF:
+                RCU_INIT_POINTER(f->bpf_prog, NULL);
+                break;
+        }
+}
+
+static void __fanout_set_data_bpf(struct packet_fanout *f, struct bpf_prog *new)
+{
+        struct bpf_prog *old;
+
+        spin_lock(&f->lock);
+        old = rcu_dereference_protected(f->bpf_prog, lockdep_is_held(&f->lock));
+        rcu_assign_pointer(f->bpf_prog, new);
+        spin_unlock(&f->lock);
+
+        if (old) {
+                synchronize_net();
+                bpf_prog_destroy(old);
+        }
+}
+
+static int fanout_set_data_cbpf(struct packet_sock *po, char __user *data,
+                                unsigned int len)
+{
+        struct bpf_prog *new;
+        struct sock_fprog fprog;
+        int ret;
+
+        if (sock_flag(&po->sk, SOCK_FILTER_LOCKED))
+                return -EPERM;
+        if (len != sizeof(fprog))
+                return -EINVAL;
+        if (copy_from_user(&fprog, data, len))
+                return -EFAULT;
+
+        ret = bpf_prog_create_from_user(&new, &fprog, NULL);
+        if (ret)
+                return ret;
+
+        __fanout_set_data_bpf(po->fanout, new);
+        return 0;
+}
+
+static int fanout_set_data(struct packet_sock *po, char __user *data,
+                           unsigned int len)
+{
+        switch (po->fanout->type) {
+        case PACKET_FANOUT_CBPF:
+                return fanout_set_data_cbpf(po, data, len);
+        default:
+                return -EINVAL;
+        };
+}
+
+static void fanout_release_data(struct packet_fanout *f)
+{
+        switch (f->type) {
+        case PACKET_FANOUT_CBPF:
+                __fanout_set_data_bpf(f, NULL);
+        };
+}
+
 static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
 {
         struct packet_sock *po = pkt_sk(sk);
@@ -1519,6 +1607,7 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
         case PACKET_FANOUT_CPU:
         case PACKET_FANOUT_RND:
         case PACKET_FANOUT_QM:
+        case PACKET_FANOUT_CBPF:
                 break;
         default:
                 return -EINVAL;
@@ -1561,10 +1650,10 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
                 match->id = id;
                 match->type = type;
                 match->flags = flags;
-                atomic_set(&match->rr_cur, 0);
                 INIT_LIST_HEAD(&match->list);
                 spin_lock_init(&match->lock);
                 atomic_set(&match->sk_ref, 0);
+                fanout_init_data(match);
                 match->prot_hook.type = po->prot_hook.type;
                 match->prot_hook.dev = po->prot_hook.dev;
                 match->prot_hook.func = packet_rcv_fanout;
@@ -1610,6 +1699,7 @@ static void fanout_release(struct sock *sk)
         if (atomic_dec_and_test(&f->sk_ref)) {
                 list_del(&f->list);
                 dev_remove_pack(&f->prot_hook);
+                fanout_release_data(f);
                 kfree(f);
         }
         mutex_unlock(&fanout_mutex);
@@ -3529,6 +3619,13 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 
                 return fanout_add(sk, val & 0xffff, val >> 16);
         }
+        case PACKET_FANOUT_DATA:
+        {
+                if (!po->fanout)
+                        return -EINVAL;
+
+                return fanout_set_data(po, optval, optlen);
+        }
         case PACKET_TX_HAS_OFF:
         {
                 unsigned int val;
diff --git a/net/packet/internal.h b/net/packet/internal.h
index e20b3e8829b8..9ee46314b7d7 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -79,7 +79,10 @@ struct packet_fanout {
         u16                     id;
         u8                      type;
         u8                      flags;
-        atomic_t                rr_cur;
+        union {
+                atomic_t                rr_cur;
+                struct bpf_prog __rcu   *bpf_prog;
+        };
         struct list_head        list;
         struct sock             *arr[PACKET_FANOUT_MAX];
         spinlock_t              lock;