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Date:   Wed, 13 Nov 2019 11:19:54 +0100
From:   Pavel Machek <pavel@denx.de>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH 4.19 062/125] ALSA: usb-audio: Fix possible NULL
 dereference at create_yamaha_midi_quirk()
Message-ID: <20191113101954.GA32553@amd>
References: <20191111181438.945353076@linuxfoundation.org>
 <20191111181448.565879068@linuxfoundation.org>
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Hi!

> From: Takashi Iwai <tiwai@suse.de>
>=20
> commit 60849562a5db4a1eee2160167e4dce4590d3eafe upstream.
>=20
> 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.

Best regards,
									Pavel

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(english) http://www.livejournal.com/~pavelmachek
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