bpf: Move dynptr type check to is_dynptr_type_expected()

Move dynptr type check to is_dynptr_type_expected() from
is_dynptr_reg_valid_init(), so that callers can better determine the cause
of a negative result (dynamic pointer not valid/initialized, dynamic
pointer of the wrong type). It will be useful for example for BTF, to
restrict which dynamic pointer types can be passed to kfuncs, as initially
only the local type will be supported.

Also, splitting makes the code more readable, since checking the dynamic
pointer type is not necessarily related to validity and initialization.

Split the validity/initialization and dynamic pointer type check also in
the verifier, and adjust the expected error message in the test (a test for
an unexpected dynptr type passed to a helper cannot be added due to missing
suitable helpers, but this case has been tested manually).

Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220920075951.929132-4-roberto.sassu@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -782,8 +782,8 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
 	return true;
 }
 
-static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
-				     enum bpf_arg_type arg_type)
+static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
+				     struct bpf_reg_state *reg)
 {
 	struct bpf_func_state *state = func(env, reg);
 	int spi = get_spi(reg->off);
@@ -799,11 +799,24 @@ static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_re
 			return false;
 	}
 
+	return true;
+}
+
+static bool is_dynptr_type_expected(struct bpf_verifier_env *env,
+				    struct bpf_reg_state *reg,
+				    enum bpf_arg_type arg_type)
+{
+	struct bpf_func_state *state = func(env, reg);
+	enum bpf_dynptr_type dynptr_type;
+	int spi = get_spi(reg->off);
+
 	/* ARG_PTR_TO_DYNPTR takes any type of dynptr */
 	if (arg_type == ARG_PTR_TO_DYNPTR)
 		return true;
 
-	return state->stack[spi].spilled_ptr.dynptr.type == arg_to_dynptr_type(arg_type);
+	dynptr_type = arg_to_dynptr_type(arg_type);
+
+	return state->stack[spi].spilled_ptr.dynptr.type == dynptr_type;
 }
 
 /* The reg state of a pointer or a bounded scalar was saved when
@@ -6095,21 +6108,27 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			}
 
 			meta->uninit_dynptr_regno = regno;
-		} else if (!is_dynptr_reg_valid_init(env, reg, arg_type)) {
+		} else if (!is_dynptr_reg_valid_init(env, reg)) {
+			verbose(env,
+				"Expected an initialized dynptr as arg #%d\n",
+				arg + 1);
+			return -EINVAL;
+		} else if (!is_dynptr_type_expected(env, reg, arg_type)) {
 			const char *err_extra = "";
 
 			switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
 			case DYNPTR_TYPE_LOCAL:
-				err_extra = "local ";
+				err_extra = "local";
 				break;
 			case DYNPTR_TYPE_RINGBUF:
-				err_extra = "ringbuf ";
+				err_extra = "ringbuf";
 				break;
 			default:
+				err_extra = "<unknown>";
 				break;
 			}
-
-			verbose(env, "Expected an initialized %sdynptr as arg #%d\n",
+			verbose(env,
+				"Expected a dynptr of type %s as arg #%d\n",
 				err_extra, arg + 1);
 			return -EINVAL;
 		}

tools/testing/selftests/bpf/prog_tests/dynptr.c

@@ -30,7 +30,7 @@ static struct {
 	{"invalid_helper2", "Expected an initialized dynptr as arg #3"},
 	{"invalid_write1", "Expected an initialized dynptr as arg #1"},
 	{"invalid_write2", "Expected an initialized dynptr as arg #3"},
-	{"invalid_write3", "Expected an initialized ringbuf dynptr as arg #1"},
+	{"invalid_write3", "Expected an initialized dynptr as arg #1"},
 	{"invalid_write4", "arg 1 is an unacquired reference"},
 	{"invalid_read1", "invalid read from stack"},
 	{"invalid_read2", "cannot pass in dynptr at an offset"},