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.
To validate the effectiveness of the framework on these new targets, we
injected two artificial bugs and let syzkaller fuzz the targets in an
attempt to catch them.
The first of these was calling the asn1 decoder with an incorrect input
from pkcs7_parse_message, like so:
- ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen);
+ ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen + 1);
The second was bug deeper inside of asn1_ber_decoder itself, like so:
- for (len = 0; n > 0; n--)
+ for (len = 0; n >= 0; n--)
syzkaller was able to trigger these bugs, and the associated KASAN
slab-out-of-bounds reports, within seconds.
The targets are defined within /lib/tests, alongside existing KUnit
tests.
Signed-off-by: Ethan Graham <ethangraham@google.com>
---
v3:
- Change the fuzz target build to depend on CONFIG_KFUZZTEST=y,
eliminating the need for a separate config option for each individual
file as suggested by Ignat Korchagin.
- Remove KFUZZTEST_EXPECT_LE on the length of the `key` field inside of
the fuzz targets. A maximum length is now set inside of the core input
parsing logic.
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/Makefile | 2 +
crypto/asymmetric_keys/tests/Makefile | 2 +
crypto/asymmetric_keys/tests/pkcs7_kfuzz.c | 22 +++++++++++
.../asymmetric_keys/tests/rsa_helper_kfuzz.c | 38 +++++++++++++++++++
4 files changed, 64 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/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-$(CONFIG_PKCS7_TEST_KEY) += pkcs7_test_key.o
pkcs7_test_key-y := \
pkcs7_key_type.o
+obj-y += tests/
+
#
# Signed PE binary-wrapped key handling
#
diff --git a/crypto/asymmetric_keys/tests/Makefile b/crypto/asymmetric_keys/tests/Makefile
new file mode 100644
index 000000000000..4ffe0bbe9530
--- /dev/null
+++ b/crypto/asymmetric_keys/tests/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_KFUZZTEST) += pkcs7_kfuzz.o
+obj-$(CONFIG_KFUZZTEST) += 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..37e02ba517d8
--- /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_ARRAY(pkcs7_parse_message_arg, data);
+ KFUZZTEST_ANNOTATE_LEN(pkcs7_parse_message_arg, datalen, data);
+
+ 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..bd29ed5e8c82
--- /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_ARRAY(rsa_parse_pub_key_arg, key);
+ KFUZZTEST_ANNOTATE_LEN(rsa_parse_pub_key_arg, key_len, key);
+
+ 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_ARRAY(rsa_parse_priv_key_arg, key);
+ KFUZZTEST_ANNOTATE_LEN(rsa_parse_priv_key_arg, key_len, key);
+
+ struct rsa_key out;
+ rsa_parse_priv_key(&out, arg->key, arg->key_len);
+}
--
2.51.0.384.g4c02a37b29-googOn Tue, Sep 16, 2025 at 11:01 AM Ethan Graham
<ethan.w.s.graham@gmail.com> wrote:
>
> 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.
>
> To validate the effectiveness of the framework on these new targets, we
> injected two artificial bugs and let syzkaller fuzz the targets in an
> attempt to catch them.
>
> The first of these was calling the asn1 decoder with an incorrect input
> from pkcs7_parse_message, like so:
>
> - ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen);
> + ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen + 1);
>
> The second was bug deeper inside of asn1_ber_decoder itself, like so:
>
> - for (len = 0; n > 0; n--)
> + for (len = 0; n >= 0; n--)
>
> syzkaller was able to trigger these bugs, and the associated KASAN
> slab-out-of-bounds reports, within seconds.
>
> The targets are defined within /lib/tests, alongside existing KUnit
> tests.
>
> Signed-off-by: Ethan Graham <ethangraham@google.com>
>
> ---
> v3:
> - Change the fuzz target build to depend on CONFIG_KFUZZTEST=y,
> eliminating the need for a separate config option for each individual
> file as suggested by Ignat Korchagin.
> - Remove KFUZZTEST_EXPECT_LE on the length of the `key` field inside of
> the fuzz targets. A maximum length is now set inside of the core input
> parsing logic.
> 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/Makefile | 2 +
> crypto/asymmetric_keys/tests/Makefile | 2 +
> crypto/asymmetric_keys/tests/pkcs7_kfuzz.c | 22 +++++++++++
> .../asymmetric_keys/tests/rsa_helper_kfuzz.c | 38 +++++++++++++++++++
> 4 files changed, 64 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/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..4ffe0bbe9530
> --- /dev/null
> +++ b/crypto/asymmetric_keys/tests/Makefile
> @@ -0,0 +1,2 @@
> +obj-$(CONFIG_KFUZZTEST) += pkcs7_kfuzz.o
> +obj-$(CONFIG_KFUZZTEST) += 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..37e02ba517d8
> --- /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_ARRAY(pkcs7_parse_message_arg, data);
> + KFUZZTEST_ANNOTATE_LEN(pkcs7_parse_message_arg, datalen, data);
> +
> + pkcs7_parse_message(arg->data, arg->datalen);
As far as I understand, this function creates an allocation, so the
fuzz test will need to free it using pkcs7_free_message() to avoid
leaking memory.
What do you think, Ignat?
> + struct rsa_key out;
> + rsa_parse_pub_key(&out, arg->key, arg->key_len);
> +}
Do we need to deallocate anything here?
Hi Ethan,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-nonmm-unstable]
[also build test WARNING on herbert-cryptodev-2.6/master herbert-crypto-2.6/master linus/master v6.17-rc6 next-20250917]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Ethan-Graham/mm-kasan-implement-kasan_poison_range/20250916-210448
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-nonmm-unstable
patch link: https://lore.kernel.org/r/20250916090109.91132-8-ethan.w.s.graham%40gmail.com
patch subject: [PATCH v1 07/10] crypto: implement KFuzzTest targets for PKCS7 and RSA parsing
config: x86_64-randconfig-121-20250918 (https://download.01.org/0day-ci/archive/20250918/202509181410.XN0MIpCh-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.4.0-5) 12.4.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250918/202509181410.XN0MIpCh-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509181410.XN0MIpCh-lkp@intel.com/
sparse warnings: (new ones prefixed by >>)
>> crypto/asymmetric_keys/tests/pkcs7_kfuzz.c:15:1: sparse: sparse: symbol '__fuzz_test__test_pkcs7_parse_message' was not declared. Should it be static?
--
>> crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c:15:1: sparse: sparse: symbol '__fuzz_test__test_rsa_parse_pub_key' was not declared. Should it be static?
>> crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c:30:1: sparse: sparse: symbol '__fuzz_test__test_rsa_parse_priv_key' was not declared. Should it be static?
vim +/__fuzz_test__test_pkcs7_parse_message +15 crypto/asymmetric_keys/tests/pkcs7_kfuzz.c
14
> 15 FUZZ_TEST(test_pkcs7_parse_message, struct pkcs7_parse_message_arg)
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi Ethan, kernel test robot noticed the following build errors: [auto build test ERROR on akpm-mm/mm-nonmm-unstable] [also build test ERROR on herbert-cryptodev-2.6/master herbert-crypto-2.6/master linus/master v6.17-rc6 next-20250917] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch#_base_tree_information] url: https://github.com/intel-lab-lkp/linux/commits/Ethan-Graham/mm-kasan-implement-kasan_poison_range/20250916-210448 base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-nonmm-unstable patch link: https://lore.kernel.org/r/20250916090109.91132-8-ethan.w.s.graham%40gmail.com patch subject: [PATCH v1 07/10] crypto: implement KFuzzTest targets for PKCS7 and RSA parsing config: x86_64-randconfig-075-20250918 (https://download.01.org/0day-ci/archive/20250918/202509180721.GaBOMCkp-lkp@intel.com/config) compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261) reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250918/202509180721.GaBOMCkp-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202509180721.GaBOMCkp-lkp@intel.com/ All errors (new ones prefixed by >>): >> ld.lld: error: undefined symbol: pkcs7_parse_message >>> referenced by pkcs7_kfuzz.c:21 (crypto/asymmetric_keys/tests/pkcs7_kfuzz.c:21) >>> vmlinux.o:(kfuzztest_write_cb_test_pkcs7_parse_message) -- >> ld.lld: error: undefined symbol: rsa_parse_pub_key >>> referenced by rsa_helper_kfuzz.c:22 (crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c:22) >>> vmlinux.o:(kfuzztest_write_cb_test_rsa_parse_pub_key) -- >> ld.lld: error: undefined symbol: rsa_parse_priv_key >>> referenced by rsa_helper_kfuzz.c:37 (crypto/asymmetric_keys/tests/rsa_helper_kfuzz.c:37) >>> vmlinux.o:(kfuzztest_write_cb_test_rsa_parse_priv_key) -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki
On Tue, Sep 16, 2025 at 10:01 AM Ethan Graham
<ethan.w.s.graham@gmail.com> wrote:
>
> 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.
>
> To validate the effectiveness of the framework on these new targets, we
> injected two artificial bugs and let syzkaller fuzz the targets in an
> attempt to catch them.
>
> The first of these was calling the asn1 decoder with an incorrect input
> from pkcs7_parse_message, like so:
>
> - ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen);
> + ret = asn1_ber_decoder(&pkcs7_decoder, ctx, data, datalen + 1);
>
> The second was bug deeper inside of asn1_ber_decoder itself, like so:
>
> - for (len = 0; n > 0; n--)
> + for (len = 0; n >= 0; n--)
>
> syzkaller was able to trigger these bugs, and the associated KASAN
> slab-out-of-bounds reports, within seconds.
>
> The targets are defined within /lib/tests, alongside existing KUnit
> tests.
>
> Signed-off-by: Ethan Graham <ethangraham@google.com>
Reviewed-by: Ignat Korchagin <ignat@cloudflare.com>
> ---
> v3:
> - Change the fuzz target build to depend on CONFIG_KFUZZTEST=y,
> eliminating the need for a separate config option for each individual
> file as suggested by Ignat Korchagin.
> - Remove KFUZZTEST_EXPECT_LE on the length of the `key` field inside of
> the fuzz targets. A maximum length is now set inside of the core input
> parsing logic.
> 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/Makefile | 2 +
> crypto/asymmetric_keys/tests/Makefile | 2 +
> crypto/asymmetric_keys/tests/pkcs7_kfuzz.c | 22 +++++++++++
> .../asymmetric_keys/tests/rsa_helper_kfuzz.c | 38 +++++++++++++++++++
> 4 files changed, 64 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/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-$(CONFIG_PKCS7_TEST_KEY) += pkcs7_test_key.o
> pkcs7_test_key-y := \
> pkcs7_key_type.o
>
> +obj-y += tests/
> +
> #
> # Signed PE binary-wrapped key handling
> #
> diff --git a/crypto/asymmetric_keys/tests/Makefile b/crypto/asymmetric_keys/tests/Makefile
> new file mode 100644
> index 000000000000..4ffe0bbe9530
> --- /dev/null
> +++ b/crypto/asymmetric_keys/tests/Makefile
> @@ -0,0 +1,2 @@
> +obj-$(CONFIG_KFUZZTEST) += pkcs7_kfuzz.o
> +obj-$(CONFIG_KFUZZTEST) += 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..37e02ba517d8
> --- /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_ARRAY(pkcs7_parse_message_arg, data);
> + KFUZZTEST_ANNOTATE_LEN(pkcs7_parse_message_arg, datalen, data);
> +
> + 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..bd29ed5e8c82
> --- /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_ARRAY(rsa_parse_pub_key_arg, key);
> + KFUZZTEST_ANNOTATE_LEN(rsa_parse_pub_key_arg, key_len, key);
> +
> + 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_ARRAY(rsa_parse_priv_key_arg, key);
> + KFUZZTEST_ANNOTATE_LEN(rsa_parse_priv_key_arg, key_len, key);
> +
> + struct rsa_key out;
> + rsa_parse_priv_key(&out, arg->key, arg->key_len);
> +}
> --
> 2.51.0.384.g4c02a37b29-goog
>
© 2016 - 2025 Red Hat, Inc.