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Message-ID: <CALrw=nGkk01xXG7S68FggsWQXygTXnXGz8AvseQuRE9K-OE0uA@mail.gmail.com>
Date: Wed, 3 Sep 2025 09:58:22 +0100
From: Ignat Korchagin <ignat@...udflare.com>
To: Ethan Graham <ethan.w.s.graham@...il.com>
Cc: ethangraham@...gle.com, glider@...gle.com, andreyknvl@...il.com,
brendan.higgins@...ux.dev, davidgow@...gle.com, dvyukov@...gle.com,
jannh@...gle.com, elver@...gle.com, rmoar@...gle.com, shuah@...nel.org,
tarasmadan@...gle.com, kasan-dev@...glegroups.com, kunit-dev@...glegroups.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, dhowells@...hat.com,
lukas@...ner.de, herbert@...dor.apana.org.au, davem@...emloft.net,
linux-crypto@...r.kernel.org
Subject: Re: [PATCH v2 RFC 7/7] crypto: implement KFuzzTest targets for PKCS7
and RSA parsing
On Mon, Sep 1, 2025 at 5:43 PM Ethan Graham <ethan.w.s.graham@...il.com> wrote:
>
> From: Ethan Graham <ethangraham@...gle.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.
nit: can I ask for another real example? AFAIK this subsystem is
rarely used (at least directly by users). However, one user-controlled
widely used parser terrifies me: load_script() function from
binfmt_script.c, which parses the shebang line for scripts. I would
really like to see what this framework can do to fuzz that.
> The targets are defined within /lib/tests, alongside existing KUnit
> tests.
>
> Signed-off-by: Ethan Graham <ethangraham@...gle.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
I'm a bit worried about the scalability of defining one (visible)
config option per fuzz file/module. Is there a use-case, where a user
would want to enable some targets, but not the others? Can it be
unconditionally enabled and compiled only if CONFIG_KFUZZTEST=y?
> + 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
>
Ignat
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