bpf: net: Add SO_DETACH_REUSEPORT_BPF

There is SO_ATTACH_REUSEPORT_[CE]BPF but there is no DETACH.
This patch adds SO_DETACH_REUSEPORT_BPF sockopt. The same
sockopt can be used to undo both SO_ATTACH_REUSEPORT_[CE]BPF.

reseport_detach_prog() is added and it is mostly a mirror
of the existing reuseport_attach_prog(). The differences are,
it does not call reuseport_alloc() and returns -ENOENT when
there is no old prog.

Cc: Craig Gallek <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Reviewed-by: Stanislav Fomichev <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>

arch/alpha/include/uapi/asm/socket.h

···
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
 
+#define SO_DETACH_REUSEPORT_BPF 68
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64

arch/mips/include/uapi/asm/socket.h

···
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
 
+#define SO_DETACH_REUSEPORT_BPF 68
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64

arch/parisc/include/uapi/asm/socket.h

···
 #define SO_RCVTIMEO_NEW         0x4040
 #define SO_SNDTIMEO_NEW         0x4041
 
+#define SO_DETACH_REUSEPORT_BPF 0x4042
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64

arch/sparc/include/uapi/asm/socket.h

···
 #define SO_RCVTIMEO_NEW          0x0044
 #define SO_SNDTIMEO_NEW          0x0045
 
+#define SO_DETACH_REUSEPORT_BPF  0x0047
+
 #if !defined(__KERNEL__)
 
 

include/net/sock_reuseport.h

···
 					  struct sk_buff *skb,
 					  int hdr_len);
 extern int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog);
+extern int reuseport_detach_prog(struct sock *sk);
+
 int reuseport_get_id(struct sock_reuseport *reuse);
 
 #endif  /* _SOCK_REUSEPORT_H */

include/uapi/asm-generic/socket.h

···
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
 
+#define SO_DETACH_REUSEPORT_BPF 68
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))

net/core/sock.c

···
 		}
 		break;
 
+	case SO_DETACH_REUSEPORT_BPF:
+		ret = reuseport_detach_prog(sk);
+		break;
+
 	case SO_DETACH_FILTER:
 		ret = sk_detach_filter(sk);
 		break;

net/core/sock_reuseport.c

···
 	return 0;
 }
 EXPORT_SYMBOL(reuseport_attach_prog);
+
+int reuseport_detach_prog(struct sock *sk)
+{
+	struct sock_reuseport *reuse;
+	struct bpf_prog *old_prog;
+
+	if (!rcu_access_pointer(sk->sk_reuseport_cb))
+		return sk->sk_reuseport ? -ENOENT : -EINVAL;
+
+	old_prog = NULL;
+	spin_lock_bh(&reuseport_lock);
+	reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
+					  lockdep_is_held(&reuseport_lock));
+	rcu_swap_protected(reuse->prog, old_prog,
+			   lockdep_is_held(&reuseport_lock));
+	spin_unlock_bh(&reuseport_lock);
+
+	if (!old_prog)
+		return -ENOENT;
+
+	sk_reuseport_prog_free(old_prog);
+	return 0;
+}
+EXPORT_SYMBOL(reuseport_detach_prog);