[PATCH bpf v2] bpf: netfilter: add BPF_NETFILTER bpf_attach_type

[Florian Westphal <fw@strlen.de>]

Andrii Nakryiko writes:

 And we currently don't have an attach type for NETLINK BPF link.
 Thankfully it's not too late to add it. I see that link_create() in
 kernel/bpf/syscall.c just bypasses attach_type check. We shouldn't
 have done that. Instead we need to add BPF_NETLINK attach type to enum
 bpf_attach_type. And wire all that properly throughout the kernel and
 libbpf itself.

This adds BPF_NETFILTER and uses it.  This breaks uabi but this
wasn't in any non-rc release yet, so it should be fine.

v2: check link_attack prog type in link_create too

Fixes: 84601d6ee68a ("bpf: add bpf_link support for BPF_NETFILTER programs")
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Link: https://lore.kernel.org/bpf/CAEf4BzZ69YgrQW7DHCJUT_X+GqMq_ZQQPBwopaJJVGFD5=d5Vg@mail.gmail.com/
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/uapi/linux/bpf.h       | 1 +
 kernel/bpf/syscall.c           | 9 +++++++++
 tools/include/uapi/linux/bpf.h | 1 +
 tools/lib/bpf/libbpf.c         | 2 +-
 4 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1bb11a6ee667..c994ff5b157c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1035,6 +1035,7 @@ enum bpf_attach_type {
 	BPF_TRACE_KPROBE_MULTI,
 	BPF_LSM_CGROUP,
 	BPF_STRUCT_OPS,
+	BPF_NETFILTER,
 	__MAX_BPF_ATTACH_TYPE
 };
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 14f39c1e573e..0c21d0d8efe4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2433,6 +2433,10 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
 		default:
 			return -EINVAL;
 		}
+	case BPF_PROG_TYPE_NETFILTER:
+		if (expected_attach_type == BPF_NETFILTER)
+			return 0;
+		return -EINVAL;
 	case BPF_PROG_TYPE_SYSCALL:
 	case BPF_PROG_TYPE_EXT:
 		if (expected_attach_type)
@@ -4590,7 +4594,12 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 
 	switch (prog->type) {
 	case BPF_PROG_TYPE_EXT:
+		break;
 	case BPF_PROG_TYPE_NETFILTER:
+		if (attr->link_create.attach_type != BPF_NETFILTER) {
+			ret = -EINVAL;
+			goto out;
+		}
 		break;
 	case BPF_PROG_TYPE_PERF_EVENT:
 	case BPF_PROG_TYPE_TRACEPOINT:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 1bb11a6ee667..c994ff5b157c 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1035,6 +1035,7 @@ enum bpf_attach_type {
 	BPF_TRACE_KPROBE_MULTI,
 	BPF_LSM_CGROUP,
 	BPF_STRUCT_OPS,
+	BPF_NETFILTER,
 	__MAX_BPF_ATTACH_TYPE
 };
 
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ad1ec893b41b..532a97cf1cc1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8712,7 +8712,7 @@ static const struct bpf_sec_def section_defs[] = {
 	SEC_DEF("struct_ops+",		STRUCT_OPS, 0, SEC_NONE),
 	SEC_DEF("struct_ops.s+",	STRUCT_OPS, 0, SEC_SLEEPABLE),
 	SEC_DEF("sk_lookup",		SK_LOOKUP, BPF_SK_LOOKUP, SEC_ATTACHABLE),
-	SEC_DEF("netfilter",		NETFILTER, 0, SEC_NONE),
+	SEC_DEF("netfilter",		NETFILTER, BPF_NETFILTER, SEC_NONE),
 };
 
 static size_t custom_sec_def_cnt;
-- 
2.39.3