Re: [PATCH 1/2] ALSA: pcm: disallow linking stream to itself

From: Takashi Iwai <tiwai@suse.de>
To: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: linux-kernel@vger.kernel.org, alsa-devel@alsa-project.org,
	Takashi Iwai <tiwai@suse.com>
Subject: Re: [PATCH 1/2] ALSA: pcm: disallow linking stream to itself
Date: Mon, 08 Jun 2020 14:48:40 +0200	[thread overview]
Message-ID: <s5h4krl67vb.wl-tiwai@suse.de> (raw)
In-Reply-To: <dc38ec162b8c83e53cf48cc8dc4dbac78667e394.1591610330.git.mirq-linux@rere.qmqm.pl>

On Mon, 08 Jun 2020 12:06:32 +0200,
Michał Mirosław wrote:
> 
> Prevent SNDRV_PCM_IOCTL_LINK linking stream to itself - the code
> can't handle it. Fixed commit is not where bug was introduced, but
> changes the context significantly.
> 
> Cc: stable@vger.kernel.org
> Fixes: 0888c321de70 ("pcm_native: switch to fdget()/fdput()")
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>

Thanks for the fix.  Just a minor point:

> @@ -2166,6 +2166,12 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
>  	}
>  	pcm_file = f.file->private_data;
>  	substream1 = pcm_file->substream;
> +
> +	if (substream == substream1) {
> +		res = -EDEADLK;

We've never used this error code, hence it may confuse the user-space
side.  I'd use a more standard -EINVAL instead; the error is basically
an invalid argument, after all.

thanks,

Takashi