[PATCH v2 bpf-next 08/13] bpf: Introduce two attach types for BPF_PROG_TYPE_SK_REUSEPORT.

[Kuniyuki Iwashima <kuniyu@amazon.co.jp>]

This commit adds new bpf_attach_type for BPF_PROG_TYPE_SK_REUSEPORT to
check if the attached eBPF program is capable of migrating sockets.

When the eBPF program is attached, the kernel runs it for socket migration
only if the expected_attach_type is BPF_SK_REUSEPORT_SELECT_OR_MIGRATE.
The kernel will change the behaviour depending on the returned value:

  - SK_PASS with selected_sk, select it as a new listener
  - SK_PASS with selected_sk NULL, fall back to the random selection
  - SK_DROP, cancel the migration

Link: https://lore.kernel.org/netdev/20201123003828.xjpjdtk4ygl6tg6h@kafai-mbp.dhcp.thefacebook.com/
Suggested-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
---
 include/uapi/linux/bpf.h       |  2 ++
 kernel/bpf/syscall.c           | 13 +++++++++++++
 tools/include/uapi/linux/bpf.h |  2 ++
 3 files changed, 17 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7a48e0055500..c7f6848c0226 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -241,6 +241,8 @@ enum bpf_attach_type {
 	BPF_XDP_CPUMAP,
 	BPF_SK_LOOKUP,
 	BPF_XDP,
+	BPF_SK_REUSEPORT_SELECT,
+	BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
 	__MAX_BPF_ATTACH_TYPE
 };
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0cd3cc2af9c1..0737673c727c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1920,6 +1920,11 @@ static void bpf_prog_load_fixup_attach_type(union bpf_attr *attr)
 			attr->expected_attach_type =
 				BPF_CGROUP_INET_SOCK_CREATE;
 		break;
+	case BPF_PROG_TYPE_SK_REUSEPORT:
+		if (!attr->expected_attach_type)
+			attr->expected_attach_type =
+				BPF_SK_REUSEPORT_SELECT;
+		break;
 	}
 }
 
@@ -2003,6 +2008,14 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
 		if (expected_attach_type == BPF_SK_LOOKUP)
 			return 0;
 		return -EINVAL;
+	case BPF_PROG_TYPE_SK_REUSEPORT:
+		switch (expected_attach_type) {
+		case BPF_SK_REUSEPORT_SELECT:
+		case BPF_SK_REUSEPORT_SELECT_OR_MIGRATE:
+			return 0;
+		default:
+			return -EINVAL;
+		}
 	case BPF_PROG_TYPE_EXT:
 		if (expected_attach_type)
 			return -EINVAL;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7a48e0055500..c7f6848c0226 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -241,6 +241,8 @@ enum bpf_attach_type {
 	BPF_XDP_CPUMAP,
 	BPF_SK_LOOKUP,
 	BPF_XDP,
+	BPF_SK_REUSEPORT_SELECT,
+	BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
 	__MAX_BPF_ATTACH_TYPE
 };
 
-- 
2.17.2 (Apple Git-113)