2024-06-10 18:40:14

by Kees Cook

Subject: [PATCH] kunit/overflow: Adjust for __counted_by with DEFINE_RAW_FLEX()

When a flexible array structure has a __counted_by annotation, its use
with DEFINE_RAW_FLEX() will result in the count being zero-initialized.
This is expected since one doesn't want to use RAW with a counted_by
struct. Adjust the tests to check for the condition and for compiler
support.

Reported-by: Christian Schrefl <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Suggested-by: Nathan Chancellor <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
---
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: [email protected]
---
lib/overflow_kunit.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
index 4ef31b0bb74d..d305b0c054bb 100644
--- a/lib/overflow_kunit.c
+++ b/lib/overflow_kunit.c
@@ -1178,14 +1178,28 @@ struct foo {
s16 array[] __counted_by(counter);
};

+struct bar {
+ int a;
+ u32 counter;
+ s16 array[];
+};
+
static void DEFINE_FLEX_test(struct kunit *test)
{
- DEFINE_RAW_FLEX(struct foo, two, array, 2);
+ /* Using _RAW_ on a __counted_by struct will initialize "counter" to zero */
+ DEFINE_RAW_FLEX(struct foo, two_but_zero, array, 2);
+#if __has_attribute(__counted_by__)
+ int expected_raw_size = sizeof(struct foo);
+#else
+ int expected_raw_size = sizeof(struct foo) + 2 * sizeof(s16);
+#endif
+ /* Without annotation, it will always be on-stack size. */
+ DEFINE_RAW_FLEX(struct bar, two, array, 2);
DEFINE_FLEX(struct foo, eight, array, counter, 8);
DEFINE_FLEX(struct foo, empty, array, counter, 0);

- KUNIT_EXPECT_EQ(test, __struct_size(two),
- sizeof(struct foo) + sizeof(s16) + sizeof(s16));
+ KUNIT_EXPECT_EQ(test, __struct_size(two_but_zero), expected_raw_size);
+ KUNIT_EXPECT_EQ(test, __struct_size(two), sizeof(struct bar) + 2 * sizeof(s16));
KUNIT_EXPECT_EQ(test, __struct_size(eight), 24);
KUNIT_EXPECT_EQ(test, __struct_size(empty), sizeof(struct foo));
}
--
2.34.1

2024-06-10 19:22:20

by Christian Schrefl

Subject: Re: [PATCH] kunit/overflow: Adjust for __counted_by with DEFINE_RAW_FLEX()

On 10.06.24 8:23 PM, Kees Cook wrote:
> When a flexible array structure has a __counted_by annotation, its use
> with DEFINE_RAW_FLEX() will result in the count being zero-initialized.
> This is expected since one doesn't want to use RAW with a counted_by
> struct. Adjust the tests to check for the condition and for compiler
> support.
>
> Reported-by: Christian Schrefl <[email protected]>
> Closes: https://lore.kernel.org/all/[email protected]/
> Suggested-by: Nathan Chancellor <[email protected]>
> Signed-off-by: Kees Cook <[email protected]>
> ---
Thanks for the quick fix!

Seems reasonable and the test passes now.

Tested-by: Christian Schrefl <[email protected]>
Reviewed-by: Christian Schrefl <[email protected]>

> Cc: "Gustavo A. R. Silva" <[email protected]>
> Cc: [email protected]
> ---
> lib/overflow_kunit.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
> index 4ef31b0bb74d..d305b0c054bb 100644
> --- a/lib/overflow_kunit.c
> +++ b/lib/overflow_kunit.c
> @@ -1178,14 +1178,28 @@ struct foo {
> s16 array[] __counted_by(counter);
> };
>
> +struct bar {
> + int a;
> + u32 counter;
> + s16 array[];
> +};
> +
> static void DEFINE_FLEX_test(struct kunit *test)
> {
> - DEFINE_RAW_FLEX(struct foo, two, array, 2);
> + /* Using _RAW_ on a __counted_by struct will initialize "counter" to zero */
> + DEFINE_RAW_FLEX(struct foo, two_but_zero, array, 2);
> +#if __has_attribute(__counted_by__)
> + int expected_raw_size = sizeof(struct foo);
> +#else
> + int expected_raw_size = sizeof(struct foo) + 2 * sizeof(s16);
> +#endif
> + /* Without annotation, it will always be on-stack size. */
> + DEFINE_RAW_FLEX(struct bar, two, array, 2);
> DEFINE_FLEX(struct foo, eight, array, counter, 8);
> DEFINE_FLEX(struct foo, empty, array, counter, 0);
>
> - KUNIT_EXPECT_EQ(test, __struct_size(two),
> - sizeof(struct foo) + sizeof(s16) + sizeof(s16));
> + KUNIT_EXPECT_EQ(test, __struct_size(two_but_zero), expected_raw_size);
> + KUNIT_EXPECT_EQ(test, __struct_size(two), sizeof(struct bar) + 2 * sizeof(s16));
> KUNIT_EXPECT_EQ(test, __struct_size(eight), 24);
> KUNIT_EXPECT_EQ(test, __struct_size(empty), sizeof(struct foo));
> }