linux-kernel - [PATCH v14 02/12] bpf: Move dynptr type check to is_dynptr_type

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Message-Id: <20220830161716.754078-3-roberto.sassu@huaweicloud.com>
Date:   Tue, 30 Aug 2022 18:17:06 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, mykolal@...com,
        dhowells@...hat.com, jarkko@...nel.org, rostedt@...dmis.org,
        mingo@...hat.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, shuah@...nel.org
Cc:     bpf@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        deso@...teo.net, memxor@...il.com,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Joanne Koong <joannelkoong@...il.com>
Subject: [PATCH v14 02/12] bpf: Move dynptr type check to is_dynptr_type_expected()

From: Roberto Sassu <roberto.sassu@...wei.com>

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).

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@...il.com>
Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 kernel/bpf/verifier.c                         | 35 ++++++++++++++-----
 .../testing/selftests/bpf/prog_tests/dynptr.c |  2 +-
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0194a36d0b36..1b913db252a3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -779,8 +779,8 @@ 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);
@@ -796,11 +796,24 @@ 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);
+	int spi = get_spi(reg->off);
+	enum bpf_dynptr_type dynptr_type;
+
 	/* 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
@@ -6050,21 +6063,27 @@ 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;
 		}
diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/testing/selftests/bpf/prog_tests/dynptr.c
index bcf80b9f7c27..8fc4e6c02bfd 100644
--- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
+++ b/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"},
-- 
2.25.1