Re: [PATCH] ASoC: ops: Fix the bounds checking in snd_soc_put_volsw_sx and snd_soc_put_xr_sx

["Tan Nayır" <tannayir@gmail.com>]

For a control defined like this:
-- SOC_SINGLE_S8_TLV("IIR0 INP0 Volume", 
WCD934X_CDC_SIDETONE_IIR0_IIR_GAIN_B1_CTL, -84, 40, digital_gain) --
This is what the snd_soc_info_volsw_sx reports:
$mc->platform_max:40, $mc->max:40, $mc->min:-84,
$uinfo->value.integer.max:40, $uinfo->value.integer.min:0

Now this is obviously wrong which is another issue which I'll explain a 
bit later
but the mixer control($mc) limits are exactly the same inside
the snd_soc_put_volsw_sx function.
So the min and max fields inside the $mc are the same in 
snd_soc_put_volsw_sx
so this means that the code without my patch has an incorrect check.

Here's an example, this is the check before the patch:
-- if (mc->platform_max && val > mc->platform_max) --
Let's say the userspace passes 50 as $val which should be within the 
range of
0 to 124 so it is a valid value.
The check is done before the val is re-scaled, so it checks whether the val
is bigger than 40 which is the value of platform_max at that point.

Is the $mc->platform_max supposed to be set to the number of steps
as opposed to the maximum value?

Back to the first issue that I've mentioned in this message, the 
snd_soc_info_volsw_sx
reports the wrong value because it adds the $mc->min to the value which 
not necessary.
Curiously enough, there are actually two commits from 6 years ago
on the Qualcomm's fork of Linux that fix this one.
Neither of these commits exist on the upstream Linux kernel at the 
moment. I've linked them below.

For the sake of integrity, all of the values that I've gathered from 
debugging
were the same before and after applying these patches.
What I mean by that is that the only thing that changes when the patches 
below are applied
is that the snd_soc_info_volsw_sx reports the correct range to the userspace
which should be 0 to 124.
Also the snd_soc_put_volsw_sx still checks the value from userspace
which has a range of 0 to 124 against the maximum of the signed range
which is from -84 to 40 regardless of the patches below.

65c7d020fbee8 ("ASoC: Update the Max value of integer controls.")
https://git.codelinaro.org/clo/la/kernel/msm-4.9/-/commit/65c7d020fbee8070f33072291c32eef7584a56d4

0d873de90eb16 ("ASoC: sound: soc: fix incorrect max value")
https://git.codelinaro.org/clo/la/kernel/msm-4.9/-/commit/0d873de90eb16e3af499eb87da1ed14440b788d5