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SubjectRe: [PATCH 4.19 062/125] ALSA: usb-audio: Fix possible NULL dereference at create_yamaha_midi_quirk()
On Wed, 13 Nov 2019 11:19:54 +0100,
Pavel Machek wrote:
>
> Hi!
>
> > From: Takashi Iwai <tiwai@suse.de>
> >
> > commit 60849562a5db4a1eee2160167e4dce4590d3eafe upstream.
> >
> > The previous addition of descriptor validation may lead to a NULL
> > dereference at create_yamaha_midi_quirk() when either injd or outjd is
> > NULL. Add proper non-NULL checks.
>
> This is wrong.
>
> > @@ -259,8 +259,8 @@ static int create_yamaha_midi_quirk(stru
> > NULL, USB_MS_MIDI_OUT_JACK);
> > if (!injd && !outjd)
> > return -ENODEV;
>
> Clearly code wants to allow at most one of them to be NULL.
>
> > - if (!snd_usb_validate_midi_desc(injd) ||
> > - !snd_usb_validate_midi_desc(outjd))
> > + if (!(injd && snd_usb_validate_midi_desc(injd)) ||
> > + !(outjd && snd_usb_validate_midi_desc(outjd)))
> > return -ENODEV;
>
> Yet it will return here if it is. Correct check would be
>
> + if (!(!injd || snd_usb_validate_midi_desc(injd)) ||
> + !(!outjd || snd_usb_validate_midi_desc(outjd)))
>
> AFAICT.

Erm, right, but a better representation is:

if ((injd && !snd_usb_validate_midi_desc(injd)) ||
(outjd && !snd_usb_validate_midi_desc(injd)))


thanks,

Takashi

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