On Mon, Jun 10, 2024 at 11:23:05AM -0700, 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 <chrisi.schr...@gmail.com>
> Closes:
> https://lore.kernel.org/all/0bfc6b38-8bc5-4971-b6fb-dc642a73f...@gmail.com/
> Suggested-by: Nathan Chancellor <nat...@kernel.org>
> Signed-off-by: Kees Cook <k...@kernel.org>
Seems reasonable to me.
Reviewed-by: Nathan Chancellor <nat...@kernel.org>
> ---
> Cc: "Gustavo A. R. Silva" <gustavo...@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> ---
> 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
>
