[PATCH v2 RFC 7/7] crypto: implement KFuzzTest targets for PKCS7 and RSA parsing

[Ethan Graham <ethan.w.s.graham@gmail.com>]

From: Ethan Graham <ethangraham@google.com>

Add KFuzzTest targets for pkcs7_parse_message, rsa_parse_pub_key, and
rsa_parse_priv_key to serve as real-world examples of how the framework is used.

These functions are ideal candidates for KFuzzTest as they perform complex
parsing of user-controlled data but are not directly exposed at the syscall
boundary. This makes them difficult to exercise with traditional fuzzing tools
and showcases the primary strength of the KFuzzTest framework: providing an
interface to fuzz internal functions.

The targets are defined within /lib/tests, alongside existing KUnit
tests.

Signed-off-by: Ethan Graham <ethangraham@google.com>

---
v2:
- Move KFuzzTest targets outside of the source files into dedicated
  _kfuzz.c files under /crypto/asymmetric_keys/tests/ as suggested by
  Ignat Korchagin and Eric Biggers.
---
---
 crypto/asymmetric_keys/Kconfig                | 15 ++++++++
 crypto/asymmetric_keys/Makefile               |  2 +
 crypto/asymmetric_keys/tests/Makefile         |  2 +
 crypto/asymmetric_keys/tests/pkcs7_kfuzz.c    | 22 +++++++++++
 .../asymmetric_keys/tests/rsa_helper_kfuzz.c  | 38 +++++++++++++++++++
 5 files changed, 79 insertions(+)
 create mode 100644 crypto/asymmetric_keys/tests/Makefile
 create mode 100644 crypto/asymmetric_keys/tests/pkcs7_kfuzz.c
 create mode 100644 crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c

diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index e1345b8f39f1..7a4c5eb18624 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -104,3 +104,18 @@ config FIPS_SIGNATURE_SELFTEST_ECDSA
 	depends on CRYPTO_ECDSA=y || CRYPTO_ECDSA=FIPS_SIGNATURE_SELFTEST
 
 endif # ASYMMETRIC_KEY_TYPE
+
+config PKCS7_MESSAGE_PARSER_KFUZZ
+	bool "Build fuzz target for PKCS#7 parser"
+	depends on KFUZZTEST
+	depends on PKCS7_MESSAGE_PARSER
+	default y
+	help
+	  Builds the KFuzzTest targets for PKCS#7.
+
+config RSA_HELPER_KFUZZ
+	bool "Build fuzz targets for RSA helpers"
+	depends on KFUZZTEST
+	default y
+	help
+	  Builds the KFuzzTest targets for RSA helper functions.
diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index bc65d3b98dcb..77b825aee6b2 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -67,6 +67,8 @@ obj-$(CONFIG_PKCS7_TEST_KEY) += pkcs7_test_key.o
 pkcs7_test_key-y := \
 	pkcs7_key_type.o
 
+obj-y += tests/
+
 #
 # Signed PE binary-wrapped key handling
 #
diff --git a/crypto/asymmetric_keys/tests/Makefile b/crypto/asymmetric_keys/tests/Makefile
new file mode 100644
index 000000000000..42a779c9042a
--- /dev/null
+++ b/crypto/asymmetric_keys/tests/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_PKCS7_MESSAGE_PARSER_KFUZZ) += pkcs7_kfuzz.o
+obj-$(CONFIG_RSA_HELPER_KFUZZ) += rsa_helper_kfuzz.o
diff --git a/crypto/asymmetric_keys/tests/pkcs7_kfuzz.c b/crypto/asymmetric_keys/tests/pkcs7_kfuzz.c
new file mode 100644
index 000000000000..84d0b0d8d0eb
--- /dev/null
+++ b/crypto/asymmetric_keys/tests/pkcs7_kfuzz.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PKCS#7 parser KFuzzTest target
+ *
+ * Copyright 2025 Google LLC
+ */
+#include <crypto/pkcs7.h>
+#include <linux/kfuzztest.h>
+
+struct pkcs7_parse_message_arg {
+	const void *data;
+	size_t datalen;
+};
+
+FUZZ_TEST(test_pkcs7_parse_message, struct pkcs7_parse_message_arg)
+{
+	KFUZZTEST_EXPECT_NOT_NULL(pkcs7_parse_message_arg, data);
+	KFUZZTEST_ANNOTATE_LEN(pkcs7_parse_message_arg, datalen, data);
+	KFUZZTEST_EXPECT_LE(pkcs7_parse_message_arg, datalen, 16 * PAGE_SIZE);
+
+	pkcs7_parse_message(arg->data, arg->datalen);
+}
diff --git a/crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c b/crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c
new file mode 100644
index 000000000000..5877e54cb75a
--- /dev/null
+++ b/crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RSA key extract helper KFuzzTest targets
+ *
+ * Copyright 2025 Google LLC
+ */
+#include <linux/kfuzztest.h>
+#include <crypto/internal/rsa.h>
+
+struct rsa_parse_pub_key_arg {
+	const void *key;
+	size_t key_len;
+};
+
+FUZZ_TEST(test_rsa_parse_pub_key, struct rsa_parse_pub_key_arg)
+{
+	KFUZZTEST_EXPECT_NOT_NULL(rsa_parse_pub_key_arg, key);
+	KFUZZTEST_ANNOTATE_LEN(rsa_parse_pub_key_arg, key_len, key);
+	KFUZZTEST_EXPECT_LE(rsa_parse_pub_key_arg, key_len, 16 * PAGE_SIZE);
+
+	struct rsa_key out;
+	rsa_parse_pub_key(&out, arg->key, arg->key_len);
+}
+
+struct rsa_parse_priv_key_arg {
+	const void *key;
+	size_t key_len;
+};
+
+FUZZ_TEST(test_rsa_parse_priv_key, struct rsa_parse_priv_key_arg)
+{
+	KFUZZTEST_EXPECT_NOT_NULL(rsa_parse_priv_key_arg, key);
+	KFUZZTEST_ANNOTATE_LEN(rsa_parse_priv_key_arg, key_len, key);
+	KFUZZTEST_EXPECT_LE(rsa_parse_priv_key_arg, key_len, 16 * PAGE_SIZE);
+
+	struct rsa_key out;
+	rsa_parse_priv_key(&out, arg->key, arg->key_len);
+}
-- 
2.51.0.318.gd7df087d1a-goog