bpf: Gate dynptr API behind CAP_BPF

This has been enabled for unprivileged programs for only one kernel
release, hence the expected annoyances due to this move are low. Users
using ringbuf can stick to non-dynptr APIs. The actual use cases dynptr
is meant to serve may not make sense in unprivileged BPF programs.

Hence, gate these helpers behind CAP_BPF and limit use to privileged
BPF programs.

Fixes: 263ae15 ("bpf: Add bpf_dynptr_from_mem for local dynptrs")
Fixes: bc34dee ("bpf: Dynptr support for ring buffers")
Fixes: 13bbbfb ("bpf: Add bpf_dynptr_read and bpf_dynptr_write")
Fixes: 34d4ef5 ("bpf: Add dynptr data slices")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220921143550.30247-1-memxor@gmail.com
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwivedi

kernel/bpf/helpers.c

@@ -1627,26 +1627,12 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_ringbuf_discard_proto;
 	case BPF_FUNC_ringbuf_query:
 		return &bpf_ringbuf_query_proto;
-	case BPF_FUNC_ringbuf_reserve_dynptr:
-		return &bpf_ringbuf_reserve_dynptr_proto;
-	case BPF_FUNC_ringbuf_submit_dynptr:
-		return &bpf_ringbuf_submit_dynptr_proto;
-	case BPF_FUNC_ringbuf_discard_dynptr:
-		return &bpf_ringbuf_discard_dynptr_proto;
 	case BPF_FUNC_for_each_map_elem:
 		return &bpf_for_each_map_elem_proto;
 	case BPF_FUNC_loop:
 		return &bpf_loop_proto;
 	case BPF_FUNC_strncmp:
 		return &bpf_strncmp_proto;
-	case BPF_FUNC_dynptr_from_mem:
-		return &bpf_dynptr_from_mem_proto;
-	case BPF_FUNC_dynptr_read:
-		return &bpf_dynptr_read_proto;
-	case BPF_FUNC_dynptr_write:
-		return &bpf_dynptr_write_proto;
-	case BPF_FUNC_dynptr_data:
-		return &bpf_dynptr_data_proto;
 	default:
 		break;
 	}
@@ -1675,6 +1661,20 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_timer_cancel_proto;
 	case BPF_FUNC_kptr_xchg:
 		return &bpf_kptr_xchg_proto;
+	case BPF_FUNC_ringbuf_reserve_dynptr:
+		return &bpf_ringbuf_reserve_dynptr_proto;
+	case BPF_FUNC_ringbuf_submit_dynptr:
+		return &bpf_ringbuf_submit_dynptr_proto;
+	case BPF_FUNC_ringbuf_discard_dynptr:
+		return &bpf_ringbuf_discard_dynptr_proto;
+	case BPF_FUNC_dynptr_from_mem:
+		return &bpf_dynptr_from_mem_proto;
+	case BPF_FUNC_dynptr_read:
+		return &bpf_dynptr_read_proto;
+	case BPF_FUNC_dynptr_write:
+		return &bpf_dynptr_write_proto;
+	case BPF_FUNC_dynptr_data:
+		return &bpf_dynptr_data_proto;
 	default:
 		break;
 	}