[PATCHv2 bpf] bpf: Force kprobe multi expected_attach_type for kprobe_multi link

[Jiri Olsa <jolsa@kernel.org>]

We currently allow to create perf link for program with
expected_attach_type == BPF_TRACE_KPROBE_MULTI.

This will cause crash when we call helpers like get_attach_cookie or
get_func_ip in such program, because it will call the kprobe_multi's
version (current->bpf_ctx context setup) of those helpers while it
expects perf_link's current->bpf_ctx context setup.

Making sure that we use BPF_TRACE_KPROBE_MULTI expected_attach_type
only for programs attaching through kprobe_multi link.

Fixes: ca74823c6e16 ("bpf: Add cookie support to programs attached with kprobe multi link")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/bpf/syscall.c | 5 +++++
 1 file changed, 5 insertions(+)

 v2 changes:
 - moved the check to bpf_prog_attach_check_attach_type [Andrii]
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0c21d0d8efe4..129cc5c276c0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3440,6 +3440,11 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
 		return prog->enforce_expected_attach_type &&
 			prog->expected_attach_type != attach_type ?
 			-EINVAL : 0;
+	case BPF_PROG_TYPE_KPROBE:
+		if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI &&
+		    attach_type != BPF_TRACE_KPROBE_MULTI)
+			return -EINVAL;
+		fallthrough;
 	default:
 		return 0;
 	}
-- 
2.41.0