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From: Nathan Chancellor <natechancellor@gmail.com>
To: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>,
	linux-media@vger.kernel.org, devel@driverdev.osuosl.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: [PATCH 6/7] media: atomisp: Avoid overflow in compute_blending
Date: Wed, 27 May 2020 00:11:49 -0700	[thread overview]
Message-ID: <20200527071150.3381228-7-natechancellor@gmail.com> (raw)
In-Reply-To: <20200527071150.3381228-1-natechancellor@gmail.com>

Clang warns:

drivers/staging/media/atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c:129:35:
warning: implicit conversion from 'unsigned long' to 'int32_t' (aka
'int') changes value from 18446744073709543424 to -8192
[-Wconstant-conversion]
        return MAX(MIN(isp_strength, 0), -XNR_BLENDING_SCALE_FACTOR);
        ~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

XNR_BLENDING_SCALE_FACTOR is BIT(13), or 8192, which will easily fit
into a signed 32-bit integer. However, it is an unsigned long, which
means that negating it is the same as subtracting that value from
ULONG_MAX + 1, which causes it to be larger than a signed 32-bit
integer so it gets implicitly converted.

We can avoid this by using the variable isp_scale, which holds the value
of XNR_BLENDING_SCALE_FACTOR already, where the implicit conversion from
unsigned long to s32 already happened. If that were to ever overflow,
clang would warn: https://godbolt.org/z/EeSxLG

Link: https://github.com/ClangBuiltLinux/linux/issues/1036
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 .../atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c      | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/media/atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c b/drivers/staging/media/atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c
index a9db6366d20b..629f07faf20a 100644
--- a/drivers/staging/media/atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c
+++ b/drivers/staging/media/atomisp/pci/isp/kernels/xnr/xnr_3.0/ia_css_xnr3.host.c
@@ -126,7 +126,7 @@ compute_blending(int strength)
 	 * exactly as s0.11 fixed point, but -1.0 can.
 	 */
 	isp_strength = -(((strength * isp_scale) + offset) / host_scale);
-	return MAX(MIN(isp_strength, 0), -XNR_BLENDING_SCALE_FACTOR);
+	return MAX(MIN(isp_strength, 0), -isp_scale);
 }
 
 void
-- 
2.27.0.rc0


  parent reply	other threads:[~2020-05-27  7:12 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-27  7:11 [PATCH 0/7] media: atomisp: Address several clang warnings Nathan Chancellor
2020-05-27  7:11 ` [PATCH 1/7] media: atomisp: Clean up if block in sh_css_sp_init_stage Nathan Chancellor
2020-05-27  7:11 ` [PATCH 2/7] media: atomisp: Remove second increment of count in atomisp_subdev_probe Nathan Chancellor
2020-05-27  7:11 ` [PATCH 3/7] media: atomisp: Add stub for atomisp_mrfld_power Nathan Chancellor
2020-05-27  7:11 ` [PATCH 4/7] media: atomisp: Remove unnecessary NULL checks in ia_css_pipe_load_extension Nathan Chancellor
2020-05-27  7:11 ` [PATCH 5/7] media: atomisp: Remove unnecessary NULL check in atomisp_param Nathan Chancellor
2020-05-27  7:11 ` Nathan Chancellor [this message]
2020-05-27  7:11 ` [PATCH 7/7] media: atomisp: Remove binary_supports_input_format Nathan Chancellor
2020-05-27  8:45 ` [PATCH 0/7] media: atomisp: Address several clang warnings Mauro Carvalho Chehab
2020-05-27 16:45   ` Nathan Chancellor
2020-05-27 17:20     ` Mauro Carvalho Chehab

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