bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write…

…_proto()

With bpf_get_probe_write_proto() no longer printing a message, we can
avoid it being a special case with its own permission check.

Refactor bpf_tracing_func_proto() similar to bpf_base_func_proto() to
have a section conditional on bpf_token_capable(CAP_SYS_ADMIN), where
the proto for bpf_probe_write_user() is returned. Finally, remove the
unnecessary bpf_get_probe_write_proto().

This simplifies the code, and adding additional CAP_SYS_ADMIN-only
helpers in future avoids duplicating the same CAP_SYS_ADMIN check.

Suggested-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Marco Elver <[email protected]>
Acked-by: Jiri Olsa <[email protected]>

kernel/trace/bpf_trace.c

@@ -357,14 +357,6 @@ static const struct bpf_func_proto bpf_probe_write_user_proto = {
 	.arg3_type	= ARG_CONST_SIZE,
 };
 
-static const struct bpf_func_proto *bpf_get_probe_write_proto(void)
-{
-	if (!capable(CAP_SYS_ADMIN))
-		return NULL;
-
-	return &bpf_probe_write_user_proto;
-}
-
 #define MAX_TRACE_PRINTK_VARARGS	3
 #define BPF_TRACE_PRINTK_SIZE		1024
 
@@ -1441,6 +1433,8 @@ late_initcall(bpf_key_sig_kfuncs_init);
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
+	const struct bpf_func_proto *func_proto;
+
 	switch (func_id) {
 	case BPF_FUNC_map_lookup_elem:
 		return &bpf_map_lookup_elem_proto;
@@ -1482,9 +1476,6 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_perf_event_read_proto;
 	case BPF_FUNC_get_prandom_u32:
 		return &bpf_get_prandom_u32_proto;
-	case BPF_FUNC_probe_write_user:
-		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
-		       NULL : bpf_get_probe_write_proto();
 	case BPF_FUNC_probe_read_user:
 		return &bpf_probe_read_user_proto;
 	case BPF_FUNC_probe_read_kernel:
@@ -1563,7 +1554,22 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_trace_vprintk:
 		return bpf_get_trace_vprintk_proto();
 	default:
-		return bpf_base_func_proto(func_id, prog);
+		break;
+	}
+
+	func_proto = bpf_base_func_proto(func_id, prog);
+	if (func_proto)
+		return func_proto;
+
+	if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN))
+		return NULL;
+
+	switch (func_id) {
+	case BPF_FUNC_probe_write_user:
+		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
+		       NULL : &bpf_probe_write_user_proto;
+	default:
+		return NULL;
 	}
 }