re: usb: gadget: Add support for USB MIDI 2.0 function driver

re: usb: gadget: Add support for USB MIDI 2.0 function driver

[Colin King (gmail)]

Hi,

Static analysis has found a minor issue in the following commit:

commit 8b645922b22303cec4628dbbbf6c8553d1cdec87
Author: Takashi Iwai <tiwai@suse.de>
Date:   Tue Jul 25 08:22:00 2023 +0200

     usb: gadget: Add support for USB MIDI 2.0 function driver

The issue is in function f_midi2_set_alt in 
drivers/usb/gadget/function/f_midi2.c as follows:

         if (intf != midi2->midi_if || alt > 1)
                 return 0;

         if (alt == 0)
                 op_mode = MIDI_OP_MODE_MIDI1;
         else if (alt == 1)
                 op_mode = MIDI_OP_MODE_MIDI2;
         else
                 op_mode = MIDI_OP_MODE_UNSET;


the first if statement will return if alt is 2 or more, so at the 
following cascaded if/else if/else statement alt is either 0 or 1, hence 
the final else that sets op_mode = MIDI_OP_MODE_UNSET can never be 
reached.

Either the last else statement is redundant and can be removed, or the 
first if statement needs to check for alt > 2 rather than > 1. I'm not 
sure which one is the valid fix to make. Any ideas?

Colin

Re: usb: gadget: Add support for USB MIDI 2.0 function driver

[Takashi Iwai]

On Thu, 07 Nov 2024 13:30:12 +0100,
Colin King (gmail) wrote:
> 
> Hi,
> 
> Static analysis has found a minor issue in the following commit:
> 
> commit 8b645922b22303cec4628dbbbf6c8553d1cdec87
> Author: Takashi Iwai <tiwai@suse.de>
> Date:   Tue Jul 25 08:22:00 2023 +0200
> 
>     usb: gadget: Add support for USB MIDI 2.0 function driver
> 
> The issue is in function f_midi2_set_alt in
> drivers/usb/gadget/function/f_midi2.c as follows:
> 
>         if (intf != midi2->midi_if || alt > 1)
>                 return 0;
> 
>         if (alt == 0)
>                 op_mode = MIDI_OP_MODE_MIDI1;
>         else if (alt == 1)
>                 op_mode = MIDI_OP_MODE_MIDI2;
>         else
>                 op_mode = MIDI_OP_MODE_UNSET;
> 
> 
> the first if statement will return if alt is 2 or more, so at the
> following cascaded if/else if/else statement alt is either 0 or 1,
> hence the final else that sets op_mode = MIDI_OP_MODE_UNSET can never
> be reached.
> 
> Either the last else statement is redundant and can be removed, or the
> first if statement needs to check for alt > 2 rather than > 1. I'm not
> sure which one is the valid fix to make. Any ideas?

We can fix in either way, as it won't happen practically :)
I guess I thought of alt < 0, but it's an unsigned int, so this is
nonsense.  I'd rather drop the redundant else statement.


thanks,

Takashi