diff mbox series

[03/32] flex_array: Add Kunit tests

Message ID 20220504014440.3697851-4-keescook@chromium.org
State New
Headers show
Series [01/32] netlink: Avoid memcpy() across flexible array boundary | expand

Commit Message

Kees Cook May 4, 2022, 1:44 a.m. UTC 
Add tests for the new flexible array structure helpers. These can be run
with:

  make ARCH=um mrproper
  ./tools/testing/kunit/kunit.py config
  ./tools/testing/kunit/kunit.py run flex_array

Cc: David Gow <davidgow@google.com>
Cc: kunit-dev@googlegroups.com
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 lib/Kconfig.debug      |  12 +-
 lib/Makefile           |   1 +
 lib/flex_array_kunit.c | 523 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 531 insertions(+), 5 deletions(-)
 create mode 100644 lib/flex_array_kunit.c

Comments

Kees Cook May 4, 2022, 7:43 p.m. UTC | #1 
On Wed, May 04, 2022 at 11:00:38AM +0800, David Gow wrote:
> On Wed, May 4, 2022 at 9:47 AM Kees Cook <keescook@chromium.org> wrote:
> >
> > Add tests for the new flexible array structure helpers. These can be run
> > with:
> >
> >   make ARCH=um mrproper
> >   ./tools/testing/kunit/kunit.py config
> 
> Nit: it shouldn't be necessary to run kunit.py config separately:
> kunit.py run will configure the kernel if necessary.

Ah yes, I think you mentioned this before. I'll adjust the commit log.

> 
> >   ./tools/testing/kunit/kunit.py run flex_array
> >
> > Cc: David Gow <davidgow@google.com>
> > Cc: kunit-dev@googlegroups.com
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> 
> This looks pretty good to me: it certainly worked on the different
> setups I tried (um, x86_64, x86_64+KASAN).
> 
> A few minor nitpicks inline, mostly around minor config-y things, or
> things which weren't totally clear on my first read-through.
> 
> Hopefully one day, with the various stubbing features or something
> similar, we'll be able to check against allocation failures in
> flex_dup(), too, but otherwise nothing seems too obviously missing.
> 
> Reviewed-by: David Gow <davidgow@google.com>

Great; thanks for the review and testing!

> 
> -- David
> 
> >  lib/Kconfig.debug      |  12 +-
> >  lib/Makefile           |   1 +
> >  lib/flex_array_kunit.c | 523 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 531 insertions(+), 5 deletions(-)
> >  create mode 100644 lib/flex_array_kunit.c
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 9077bb38bc93..8bae6b169c50 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -2551,11 +2551,6 @@ config OVERFLOW_KUNIT_TEST
> >           Builds unit tests for the check_*_overflow(), size_*(), allocation, and
> >           related functions.
> >
> > -         For more information on KUnit and unit tests in general please refer
> > -         to the KUnit documentation in Documentation/dev-tools/kunit/.
> > -
> > -         If unsure, say N.
> > -
> 
> Nit: while I'm not against removing some of this boilerplate, is it
> better suited for a separate commit?

Make sense, yes. I'll drop this for now.

> 
> >  config STACKINIT_KUNIT_TEST
> >         tristate "Test level of stack variable initialization" if !KUNIT_ALL_TESTS
> >         depends on KUNIT
> > @@ -2567,6 +2562,13 @@ config STACKINIT_KUNIT_TEST
> >           CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
> >           or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
> >
> > +config FLEX_ARRAY_KUNIT_TEST
> > +       tristate "Test flex_*() family of helper functions at runtime" if !KUNIT_ALL_TESTS
> > +       depends on KUNIT
> > +       default KUNIT_ALL_TESTS
> > +       help
> > +         Builds unit tests for flexible array copy helper functions.
> > +
> 
> Nit: checkpatch warns that the description here may be insufficient:
> WARNING: please write a help paragraph that fully describes the config symbol

Yeah, I don't know anything to put here that isn't just more
boilerplate, so I'm choosing to ignore this for now. :)

> > [...]
> > +struct normal {
> > +       size_t  datalen;
> > +       u32     data[];
> > +};
> > +
> > +struct decl_normal {
> > +       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, datalen);
> > +       DECLARE_FLEX_ARRAY_ELEMENTS(u32, data);
> > +};
> > +
> > +struct aligned {
> > +       unsigned short  datalen;
> > +       char            data[] __aligned(__alignof__(u64));
> > +};
> > +
> > +struct decl_aligned {
> > +       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(unsigned short, datalen);
> > +       DECLARE_FLEX_ARRAY_ELEMENTS(char, data) __aligned(__alignof__(u64));
> > +};
> > +
> > +static void struct_test(struct kunit *test)
> > +{
> > +       COMPARE_STRUCTS(struct normal, struct decl_normal);
> > +       COMPARE_STRUCTS(struct aligned, struct decl_aligned);
> > +}
> 
> If I understand it, the purpose of this is to ensure that structs both
> with and without the flexible array declaration have the same memory
> layout?
> 
> If so, any chance of a comment briefly stating that's the purpose (or
> renaming this test struct_layout_test())?

Yeah, good idea; I'll improve the naming.

> 
> Also, would it make sense to do the same with the struct with internal
> padding below?

Heh, yes, good point! :)

> [...]
> > +#define CHECK_COPY(ptr)                do {                                            \
> > +       typeof(*(ptr)) *_cc_dst = (ptr);                                        \
> > +       KUNIT_EXPECT_EQ(test, _cc_dst->induce_padding, 0);                      \
> > +       memcpy(&padding, &_cc_dst->induce_padding + sizeof(_cc_dst->induce_padding), \
> > +              sizeof(padding));                                                \
> > +       /* Padding should be zero too. */                                       \
> > +       KUNIT_EXPECT_EQ(test, padding, 0);                                      \
> > +       KUNIT_EXPECT_EQ(test, src->count, _cc_dst->count);                      \
> > +       KUNIT_EXPECT_EQ(test, _cc_dst->count, TEST_TARGET);                     \
> > +       for (i = 0; i < _cc_dst->count - 1; i++) {                              \
> > +               /* 'A' is 0x41, and here repeated in a u32. */                  \
> 
> Would it be simpler to just note that the magic value is 0x41, rather
> than have it be the character 'A'?

Yeah, now fixed.

> [...]
> > +       CHECK_COPY(&encap->fas);
> > +       /* Check that items external to "fas" are zero. */
> > +       KUNIT_EXPECT_EQ(test, encap->flags, 0);
> > +       KUNIT_EXPECT_EQ(test, encap->junk, 0);
> > +       kfree(encap);
> > +#undef MAGIC_WORD
> 
> MAGIC_WORD isn't defined (or used) for flux_dup_test? Is it worth
> using it (or something similar) for the 'A' / 0x14141414 and the
> CHECK_COPY() macro?

Oops, yes. Fixed.

Thanks again!

-Kees
diff mbox series

Patch

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9077bb38bc93..8bae6b169c50 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2551,11 +2551,6 @@  config OVERFLOW_KUNIT_TEST
 	  Builds unit tests for the check_*_overflow(), size_*(), allocation, and
 	  related functions.
 
-	  For more information on KUnit and unit tests in general please refer
-	  to the KUnit documentation in Documentation/dev-tools/kunit/.
-
-	  If unsure, say N.
-
 config STACKINIT_KUNIT_TEST
 	tristate "Test level of stack variable initialization" if !KUNIT_ALL_TESTS
 	depends on KUNIT
@@ -2567,6 +2562,13 @@  config STACKINIT_KUNIT_TEST
 	  CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
 	  or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
 
+config FLEX_ARRAY_KUNIT_TEST
+	tristate "Test flex_*() family of helper functions at runtime" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Builds unit tests for flexible array copy helper functions.
+
 config TEST_UDELAY
 	tristate "udelay test driver"
 	help
diff --git a/lib/Makefile b/lib/Makefile
index 6b9ffc1bd1ee..9884318db330 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -366,6 +366,7 @@  obj-$(CONFIG_MEMCPY_KUNIT_TEST) += memcpy_kunit.o
 obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
 CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
 obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
+obj-$(CONFIG_FLEX_ARRAY_KUNIT_TEST) += flex_array_kunit.o
 
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 
diff --git a/lib/flex_array_kunit.c b/lib/flex_array_kunit.c
new file mode 100644
index 000000000000..48bee88945b4
--- /dev/null
+++ b/lib/flex_array_kunit.c
@@ -0,0 +1,523 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for flex_*() array manipulation helpers.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/flex_array.h>
+
+#define COMPARE_STRUCTS(STRUCT_A, STRUCT_B)	do {			\
+	STRUCT_A *ptr_A;						\
+	STRUCT_B *ptr_B;						\
+	int rc;								\
+	size_t size_A, size_B;						\
+									\
+	/* matching types for flex array elements and count */		\
+	KUNIT_EXPECT_EQ(test, sizeof(*ptr_A), sizeof(*ptr_B));		\
+	KUNIT_EXPECT_TRUE(test, __same_type(*ptr_A->data,		\
+		*ptr_B->__flex_array_elements));			\
+	KUNIT_EXPECT_TRUE(test, __same_type(ptr_A->datalen,		\
+		ptr_B->__flex_array_elements_count));			\
+	KUNIT_EXPECT_EQ(test, sizeof(*ptr_A->data),			\
+			      sizeof(*ptr_B->__flex_array_elements));	\
+	KUNIT_EXPECT_EQ(test, offsetof(typeof(*ptr_A), data),		\
+			      offsetof(typeof(*ptr_B),			\
+				       __flex_array_elements));		\
+	KUNIT_EXPECT_EQ(test, offsetof(typeof(*ptr_A), datalen),	\
+			      offsetof(typeof(*ptr_B),			\
+				       __flex_array_elements_count));	\
+									\
+	/* struct_size() vs __fas_bytes() */				\
+	size_A = struct_size(ptr_A, data, 13);				\
+	rc = __fas_bytes(ptr_B, __flex_array_elements,			\
+			 __flex_array_elements_count, 13, &size_B);	\
+	KUNIT_EXPECT_EQ(test, rc, 0);					\
+	KUNIT_EXPECT_EQ(test, size_A, size_B);				\
+									\
+	/* flex_array_size() vs __fas_elements_bytes() */		\
+	size_A = flex_array_size(ptr_A, data, 13);			\
+	rc = __fas_elements_bytes(ptr_B, __flex_array_elements,		\
+			 __flex_array_elements_count, 13, &size_B);	\
+	KUNIT_EXPECT_EQ(test, rc, 0);					\
+	KUNIT_EXPECT_EQ(test, size_A, size_B);				\
+									\
+	KUNIT_EXPECT_EQ(test, sizeof(*ptr_A) + size_A,			\
+			      offsetof(typeof(*ptr_A), data) +		\
+			      (sizeof(*ptr_A->data) * 13));		\
+	KUNIT_EXPECT_EQ(test, sizeof(*ptr_B) + size_B,			\
+			      offsetof(typeof(*ptr_B),			\
+				       __flex_array_elements) +		\
+			      (sizeof(*ptr_B->__flex_array_elements) *	\
+			       13));					\
+} while (0)
+
+struct normal {
+	size_t	datalen;
+	u32	data[];
+};
+
+struct decl_normal {
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, datalen);
+	DECLARE_FLEX_ARRAY_ELEMENTS(u32, data);
+};
+
+struct aligned {
+	unsigned short	datalen;
+	char		data[] __aligned(__alignof__(u64));
+};
+
+struct decl_aligned {
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(unsigned short, datalen);
+	DECLARE_FLEX_ARRAY_ELEMENTS(char, data) __aligned(__alignof__(u64));
+};
+
+static void struct_test(struct kunit *test)
+{
+	COMPARE_STRUCTS(struct normal, struct decl_normal);
+	COMPARE_STRUCTS(struct aligned, struct decl_aligned);
+}
+
+/* Flexible array structure with internal padding. */
+struct flex_cpy_obj {
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(u8, count);
+	unsigned long empty;
+	char induce_padding;
+	/* padding ends up here */
+	unsigned long after_padding;
+	DECLARE_FLEX_ARRAY_ELEMENTS(u32, flex);
+};
+
+/* Encapsulating flexible array structure. */
+struct flex_dup_obj {
+	unsigned long flags;
+	int junk;
+	struct flex_cpy_obj fas;
+};
+
+/* Flexible array struct of only bytes. */
+struct tiny_flex {
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(u8, count);
+	DECLARE_FLEX_ARRAY_ELEMENTS(u8, byte_array);
+};
+
+#define CHECK_COPY(ptr)		do {						\
+	typeof(*(ptr)) *_cc_dst = (ptr);					\
+	KUNIT_EXPECT_EQ(test, _cc_dst->induce_padding, 0);			\
+	memcpy(&padding, &_cc_dst->induce_padding + sizeof(_cc_dst->induce_padding), \
+	       sizeof(padding));						\
+	/* Padding should be zero too. */					\
+	KUNIT_EXPECT_EQ(test, padding, 0);					\
+	KUNIT_EXPECT_EQ(test, src->count, _cc_dst->count);			\
+	KUNIT_EXPECT_EQ(test, _cc_dst->count, TEST_TARGET);			\
+	for (i = 0; i < _cc_dst->count - 1; i++) {				\
+		/* 'A' is 0x41, and here repeated in a u32. */			\
+		KUNIT_EXPECT_EQ(test, _cc_dst->flex[i], 0x41414141);		\
+	}									\
+	/* Last item should be different. */					\
+	KUNIT_EXPECT_EQ(test, _cc_dst->flex[_cc_dst->count - 1], 0x14141414);	\
+} while (0)
+
+/* Test copying from one flexible array struct into another. */
+static void flex_cpy_test(struct kunit *test)
+{
+#define TEST_BOUNDS	13
+#define TEST_TARGET	12
+#define TEST_SMALL	10
+	struct flex_cpy_obj *src, *dst;
+	unsigned long padding;
+	int i, rc;
+
+	/* Prepare open-coded source. */
+	src = kzalloc(struct_size(src, flex, TEST_BOUNDS), GFP_KERNEL);
+	src->count = TEST_BOUNDS;
+	memset(src->flex, 'A', flex_array_size(src, flex, TEST_BOUNDS));
+	src->flex[src->count - 2] = 0x14141414;
+	src->flex[src->count - 1] = 0x24242424;
+
+	/* Prepare open-coded destination, alloc only. */
+	dst = kzalloc(struct_size(src, flex, TEST_BOUNDS), GFP_KERNEL);
+	/* Pre-fill with 0xFE marker. */
+	memset(dst, 0xFE, struct_size(src, flex, TEST_BOUNDS));
+	/* Pretend we're 1 element smaller. */
+	dst->count = TEST_TARGET;
+
+	/* Pretend to match the target destination size. */
+	src->count = TEST_TARGET;
+
+	rc = flex_cpy(dst, src);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	CHECK_COPY(dst);
+	/* Item past last copied item is unchanged from initial memset. */
+	KUNIT_EXPECT_EQ(test, dst->flex[dst->count], 0xFEFEFEFE);
+
+	/* Now trip overflow, and verify we didn't clobber beyond end. */
+	src->count = TEST_BOUNDS;
+	rc = flex_cpy(dst, src);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Item past last copied item is unchanged from initial memset. */
+	KUNIT_EXPECT_EQ(test, dst->flex[dst->count], 0xFEFEFEFE);
+
+	/* Reset destination contents. */
+	memset(dst, 0xFD, struct_size(src, flex, TEST_BOUNDS));
+	dst->count = TEST_TARGET;
+
+	/* Copy less than max. */
+	src->count = TEST_SMALL;
+	rc = flex_cpy(dst, src);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	/* Verify count was adjusted. */
+	KUNIT_EXPECT_EQ(test, dst->count, TEST_SMALL);
+	/* Verify element beyond src size was wiped. */
+	KUNIT_EXPECT_EQ(test, dst->flex[TEST_SMALL], 0);
+	/* Verify element beyond original dst size was untouched. */
+	KUNIT_EXPECT_EQ(test, dst->flex[TEST_TARGET], 0xFDFDFDFD);
+
+	kfree(dst);
+	kfree(src);
+#undef TEST_BOUNDS
+#undef TEST_TARGET
+#undef TEST_SMALL
+}
+
+static void flex_dup_test(struct kunit *test)
+{
+#define TEST_TARGET	12
+	struct flex_cpy_obj *src, *dst = NULL, **null = NULL;
+	struct flex_dup_obj *encap = NULL;
+	unsigned long padding;
+	int i, rc;
+
+	/* Prepare open-coded source. */
+	src = kzalloc(struct_size(src, flex, TEST_TARGET), GFP_KERNEL);
+	src->count = TEST_TARGET;
+	memset(src->flex, 'A', flex_array_size(src, flex, TEST_TARGET));
+	src->flex[src->count - 1] = 0x14141414;
+
+	/* Reject NULL @alloc. */
+	rc = flex_dup(null, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+
+	/* Check good copy. */
+	rc = flex_dup(&dst, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_ASSERT_TRUE(test, dst != NULL);
+	CHECK_COPY(dst);
+
+	/* Reject non-NULL *@alloc. */
+	rc = flex_dup(&dst, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+
+	kfree(dst);
+
+	/* Check good encap copy. */
+	rc = __flex_dup(&encap, .fas, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_ASSERT_TRUE(test, dst != NULL);
+	CHECK_COPY(&encap->fas);
+	/* Check that items external to "fas" are zero. */
+	KUNIT_EXPECT_EQ(test, encap->flags, 0);
+	KUNIT_EXPECT_EQ(test, encap->junk, 0);
+	kfree(encap);
+#undef MAGIC_WORD
+#undef TEST_TARGET
+}
+
+static void mem_to_flex_test(struct kunit *test)
+{
+#define TEST_TARGET	9
+#define TEST_MAX	U8_MAX
+#define MAGIC_WORD	0x03030303
+	u8 magic_byte = MAGIC_WORD & 0xff;
+	struct flex_cpy_obj *dst;
+	size_t big = (size_t)INT_MAX + 1;
+	char small[] = "Hello";
+	char *src;
+	u32 src_len;
+	int rc;
+
+	/* Open coded allocations, 1 larger than actually used. */
+	src_len = flex_array_size(dst, flex, TEST_MAX + 1);
+	src = kzalloc(src_len, GFP_KERNEL);
+	dst = kzalloc(struct_size(dst, flex, TEST_MAX + 1), GFP_KERNEL);
+	dst->count = TEST_TARGET;
+
+	/* Fill source. */
+	memset(src, magic_byte, src_len);
+
+	/* Short copy is fine. */
+	KUNIT_EXPECT_EQ(test, dst->flex[0], 0);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+	rc = mem_to_flex(dst, src, 1);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_EXPECT_EQ(test, dst->count, 1);
+	KUNIT_EXPECT_EQ(test, dst->after_padding, 0);
+	KUNIT_EXPECT_EQ(test, dst->flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+	dst->count = TEST_TARGET;
+
+	/* Reject negative elements count. */
+	rc = mem_to_flex(dst, small, -1);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure dst is unchanged. */
+	KUNIT_EXPECT_EQ(test, dst->flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+
+	/* Reject compile-time read overflow. */
+	rc = mem_to_flex(dst, small, 20);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure dst is unchanged. */
+	KUNIT_EXPECT_EQ(test, dst->flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+
+	/* Reject giant buffer source. */
+	rc = mem_to_flex(dst, small, big);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure dst is unchanged. */
+	KUNIT_EXPECT_EQ(test, dst->flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+
+	/* Copy beyond storage size is rejected. */
+	dst->count = TEST_MAX;
+	KUNIT_EXPECT_EQ(test, dst->flex[TEST_MAX - 1], 0);
+	KUNIT_EXPECT_EQ(test, dst->flex[TEST_MAX], 0);
+	rc = mem_to_flex(dst, src, TEST_MAX + 1);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure dst is unchanged. */
+	KUNIT_EXPECT_EQ(test, dst->flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, dst->flex[1], 0);
+
+	kfree(dst);
+	kfree(src);
+#undef MAGIC_WORD
+#undef TEST_MAX
+#undef TEST_TARGET
+}
+
+static void mem_to_flex_dup_test(struct kunit *test)
+{
+#define ELEMENTS_COUNT	259
+#define MAGIC_WORD	0xABABABAB
+	u8 magic_byte = MAGIC_WORD & 0xff;
+	struct flex_dup_obj *obj = NULL;
+	struct tiny_flex *tiny = NULL, **null = NULL;
+	size_t src_len, count, big = (size_t)INT_MAX + 1;
+	char small[] = "Hello";
+	u8 *src;
+	int rc;
+
+	src_len = struct_size(tiny, byte_array, ELEMENTS_COUNT);
+	src = kzalloc(src_len, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, src != NULL);
+	/* Fill with bytes. */
+	memset(src, magic_byte, src_len);
+	KUNIT_EXPECT_EQ(test, src[0], magic_byte);
+	KUNIT_EXPECT_EQ(test, src[src_len / 2], magic_byte);
+	KUNIT_EXPECT_EQ(test, src[src_len - 1], magic_byte);
+
+	/* Reject storage exceeding elements_count type. */
+	count = ELEMENTS_COUNT;
+	rc = mem_to_flex_dup(&tiny, src, count, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	KUNIT_EXPECT_TRUE(test, tiny == NULL);
+
+	/* Reject negative elements count. */
+	rc = mem_to_flex_dup(&tiny, src, -1, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	KUNIT_EXPECT_TRUE(test, tiny == NULL);
+
+	/* Reject compile-time read overflow. */
+	rc = mem_to_flex_dup(&tiny, small, 20, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	KUNIT_EXPECT_TRUE(test, tiny == NULL);
+
+	/* Reject giant buffer source. */
+	rc = mem_to_flex_dup(&tiny, small, big, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	KUNIT_EXPECT_TRUE(test, tiny == NULL);
+
+	/* Reject NULL @alloc. */
+	rc = mem_to_flex_dup(null, src, count, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+
+	/* Allow reasonable count.*/
+	count = ELEMENTS_COUNT / 2;
+	rc = mem_to_flex_dup(&tiny, src, count, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_ASSERT_TRUE(test, tiny != NULL);
+	/* Spot check the copy happened. */
+	KUNIT_EXPECT_EQ(test, tiny->count, count);
+	KUNIT_EXPECT_EQ(test, tiny->byte_array[0], magic_byte);
+	KUNIT_EXPECT_EQ(test, tiny->byte_array[count / 2], magic_byte);
+	KUNIT_EXPECT_EQ(test, tiny->byte_array[count - 1], magic_byte);
+
+	/* Reject non-NULL *@alloc. */
+	rc = mem_to_flex_dup(&tiny, src, count, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+	kfree(tiny);
+
+	/* Works with encapsulation too. */
+	count = ELEMENTS_COUNT / 10;
+	rc = __mem_to_flex_dup(&obj, .fas, src, count, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_ASSERT_TRUE(test, obj != NULL);
+	/* Spot check the copy happened. */
+	KUNIT_EXPECT_EQ(test, obj->fas.count, count);
+	KUNIT_EXPECT_EQ(test, obj->fas.after_padding, 0);
+	KUNIT_EXPECT_EQ(test, obj->fas.flex[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, obj->fas.flex[count / 2], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, obj->fas.flex[count - 1], MAGIC_WORD);
+	/* Check members before flexible array struct are zero. */
+	KUNIT_EXPECT_EQ(test, obj->flags, 0);
+	KUNIT_EXPECT_EQ(test, obj->junk, 0);
+	kfree(obj);
+#undef MAGIC_WORD
+#undef ELEMENTS_COUNT
+}
+
+static void flex_to_mem_test(struct kunit *test)
+{
+#define ELEMENTS_COUNT	200
+#define MAGIC_WORD	0xF1F2F3F4
+	struct flex_cpy_obj *src;
+	typeof(*src->flex) *cast;
+	size_t src_len = struct_size(src, flex, ELEMENTS_COUNT);
+	size_t copy_len = flex_array_size(src, flex, ELEMENTS_COUNT);
+	int i, rc;
+	size_t bytes = 0;
+	u8 too_small;
+	u8 *dst;
+
+	/* Create a filled flexible array struct. */
+	src = kzalloc(src_len, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, src != NULL);
+	src->count = ELEMENTS_COUNT;
+	src->after_padding = 13;
+	for (i = 0; i < ELEMENTS_COUNT; i++)
+		src->flex[i] = MAGIC_WORD;
+
+	/* Over-allocate space to do past-src_len checking. */
+	dst = kzalloc(src_len * 2, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, dst != NULL);
+	cast = (void *)dst;
+
+	/* Fail if dst is too small. */
+	rc = flex_to_mem(dst, copy_len - 1, src, &bytes);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure nothing was copied. */
+	KUNIT_EXPECT_EQ(test, bytes, 0);
+	KUNIT_EXPECT_EQ(test, cast[0], 0);
+
+	/* Fail if type too small to hold size of copy. */
+	KUNIT_EXPECT_GT(test, copy_len, type_max(typeof(too_small)));
+	rc = flex_to_mem(dst, copy_len, src, &too_small);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	/* Make sure nothing was copied. */
+	KUNIT_EXPECT_EQ(test, bytes, 0);
+	KUNIT_EXPECT_EQ(test, cast[0], 0);
+
+	/* Check good copy. */
+	rc = flex_to_mem(dst, copy_len, src, &bytes);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_EXPECT_EQ(test, bytes, copy_len);
+	/* Spot check the copy */
+	KUNIT_EXPECT_EQ(test, cast[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, cast[ELEMENTS_COUNT / 2], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, cast[ELEMENTS_COUNT - 1], MAGIC_WORD);
+	/* Make sure nothing was written after last element. */
+	KUNIT_EXPECT_EQ(test, cast[ELEMENTS_COUNT], 0);
+
+	kfree(dst);
+	kfree(src);
+#undef MAGIC_WORD
+#undef ELEMENTS_COUNT
+}
+
+static void flex_to_mem_dup_test(struct kunit *test)
+{
+#define ELEMENTS_COUNT	210
+#define MAGIC_WORD	0xF0F1F2F3
+	struct flex_dup_obj *obj, **null = NULL;
+	struct flex_cpy_obj *src;
+	typeof(*src->flex) *cast;
+	size_t obj_len = struct_size(obj, fas.flex, ELEMENTS_COUNT);
+	size_t src_len = struct_size(src, flex, ELEMENTS_COUNT);
+	size_t copy_len = flex_array_size(src, flex, ELEMENTS_COUNT);
+	int i, rc;
+	size_t bytes = 0;
+	u8 too_small = 0;
+	u8 *dst = NULL;
+
+	/* Create a filled flexible array struct. */
+	obj = kzalloc(obj_len, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, obj != NULL);
+	obj->fas.count = ELEMENTS_COUNT;
+	obj->fas.after_padding = 13;
+	for (i = 0; i < ELEMENTS_COUNT; i++)
+		obj->fas.flex[i] = MAGIC_WORD;
+	src = &obj->fas;
+
+	/* Fail if type too small to hold size of copy. */
+	KUNIT_EXPECT_GT(test, src_len, type_max(typeof(too_small)));
+	rc = flex_to_mem_dup(&dst, &too_small, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -E2BIG);
+	KUNIT_EXPECT_TRUE(test, dst == NULL);
+	KUNIT_EXPECT_EQ(test, too_small, 0);
+
+	/* Fail if @alloc_size is NULL. */
+	KUNIT_EXPECT_TRUE(test, dst == NULL);
+	rc = flex_to_mem_dup(&dst, dst, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+	KUNIT_EXPECT_TRUE(test, dst == NULL);
+
+	/* Fail if @alloc is NULL. */
+	rc = flex_to_mem_dup(null, &bytes, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+	KUNIT_EXPECT_TRUE(test, dst == NULL);
+	KUNIT_EXPECT_EQ(test, bytes, 0);
+
+	/* Check good copy. */
+	rc = flex_to_mem_dup(&dst, &bytes, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, 0);
+	KUNIT_EXPECT_TRUE(test, dst != NULL);
+	KUNIT_EXPECT_EQ(test, bytes, copy_len);
+	cast = (void *)dst;
+	/* Spot check the copy */
+	KUNIT_EXPECT_EQ(test, cast[0], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, cast[ELEMENTS_COUNT / 2], MAGIC_WORD);
+	KUNIT_EXPECT_EQ(test, cast[ELEMENTS_COUNT - 1], MAGIC_WORD);
+
+	/* Fail if *@alloc is non-NULL. */
+	bytes = 0;
+	rc = flex_to_mem_dup(&dst, &bytes, src, GFP_KERNEL);
+	KUNIT_EXPECT_EQ(test, rc, -EINVAL);
+	KUNIT_EXPECT_EQ(test, bytes, 0);
+
+	kfree(dst);
+	kfree(obj);
+#undef MAGIC_WORD
+#undef ELEMENTS_COUNT
+}
+
+static struct kunit_case flex_array_test_cases[] = {
+	KUNIT_CASE(struct_test),
+	KUNIT_CASE(flex_cpy_test),
+	KUNIT_CASE(flex_dup_test),
+	KUNIT_CASE(mem_to_flex_test),
+	KUNIT_CASE(mem_to_flex_dup_test),
+	KUNIT_CASE(flex_to_mem_test),
+	KUNIT_CASE(flex_to_mem_dup_test),
+	{}
+};
+
+static struct kunit_suite flex_array_test_suite = {
+	.name = "flex_array",
+	.test_cases = flex_array_test_cases,
+};
+
+kunit_test_suite(flex_array_test_suite);
+
+MODULE_LICENSE("GPL");