linux-kernel - Re: [PATCH] drm: tests: Fix a buffer overflow in format_helper

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Message-ID: <20221019172919.GA5336@elementary>
Date:   Wed, 19 Oct 2022 19:29:19 +0200
From:   José Expósito <jose.exposito89@...il.com>
To:     David Gow <davidgow@...gle.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <maxime@...no.tech>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Maíra Canal <mairacanal@...eup.net>,
        dri-devel@...ts.freedesktop.org, Sam Ravnborg <sam@...nborg.org>,
        linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        javierm@...hat.com
Subject: Re: [PATCH] drm: tests: Fix a buffer overflow in format_helper_test

On Wed, Oct 19, 2022 at 03:32:40PM +0800, David Gow wrote:
> The xrgb2101010 format conversion test (unlike for other formats) does
> an endianness conversion on the results. However, it always converts
> TEST_BUF_SIZE 32-bit integers, which results in reading from (and
> writing to) more memory than in present in the result buffer. Instead,
> use the buffer size, divided by sizeof(u32).
> 
> The issue could be reproduced with KASAN:
> ./tools/testing/kunit/kunit.py run --kunitconfig drivers/gpu/drm/tests \
> 	--kconfig_add CONFIG_KASAN=y --kconfig_add CONFIG_KASAN_VMALLOC=y \
> 	--kconfig_add CONFIG_KASAN_KUNIT_TEST=y \
> 	drm_format_helper_test.*xrgb2101010
> 
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Fixes: 453114319699 ("drm/format-helper: Add KUnit tests for drm_fb_xrgb8888_to_xrgb2101010()")
> Signed-off-by: David Gow <davidgow@...gle.com>
> ---
> 
> This is a fix for the issue reported here:
> https://lore.kernel.org/dri-devel/CA+G9fYsuc9G+RO81E=vHMqxYStsmLURLdOB0NF26kJ1=K8pRZA@mail.gmail.com/
> 
> Note that it may conflict with the KUNIT_EXPECT_MEMEQ() series here:
> https://lore.kernel.org/linux-kselftest/20221018190541.189780-1-mairacanal@riseup.net/
> 
> Cheers,
> -- David
> 
> ---
>  drivers/gpu/drm/tests/drm_format_helper_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tests/drm_format_helper_test.c b/drivers/gpu/drm/tests/drm_format_helper_test.c
> index 8d86c250c2ec..2191e57f2297 100644
> --- a/drivers/gpu/drm/tests/drm_format_helper_test.c
> +++ b/drivers/gpu/drm/tests/drm_format_helper_test.c
> @@ -438,7 +438,7 @@ static void drm_test_fb_xrgb8888_to_xrgb2101010(struct kunit *test)
>  	iosys_map_set_vaddr(&src, xrgb8888);
>  
>  	drm_fb_xrgb8888_to_xrgb2101010(&dst, &result->dst_pitch, &src, &fb, &params->clip);
> -	buf = le32buf_to_cpu(test, buf, TEST_BUF_SIZE);
> +	buf = le32buf_to_cpu(test, buf, dst_size / sizeof(u32));
>  	KUNIT_EXPECT_EQ(test, memcmp(buf, result->expected, dst_size), 0);
>  }

Thanks a lot for fixing this bug David, I just tested it and
worked as expected.

Do you think that we should update the other calls to
le32buf_to_cpu() to follow a similar approach?

Regardless of a possible follow up patch:
Reviewed-by: José Expósito <jose.exposito89@...il.com>

Jose

>  
> -- 
> 2.38.0.413.g74048e4d9e-goog
>