tree 311778d94f0631930e6bd4fd690e00e025565475
parent 541f681340c4248ce49f4dbaa64ce227914ad5e7
author Nathan Chancellor <natechancellor@gmail.com> 1590563509 +0200
committer Mauro Carvalho Chehab <mchehab+huawei@kernel.org> 1591892355 +0200

media: atomisp: Avoid overflow in compute_blending

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>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>