[PATCH 4.19.y] ALSA: pcm: disallow linking stream to itself

[PATCH 4.19.y] ALSA: pcm: disallow linking stream to itself

[Takashi Iwai]

From: Michał Mirosław <mirq-linux@rere.qmqm.pl>

commit 951e2736f4b11b58dc44d41964fa17c3527d882a upstream.

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>
Link: https://lore.kernel.org/r/89c4a2487609a0ed6af3ecf01cc972bdc59a7a2d.1591634956.git.mirq-linux@rere.qmqm.pl
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---

Backported to 4.19.y.  It can be used for older branches, too.

 sound/core/pcm_native.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 14b1ee29509d..071e09c3d855 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1950,6 +1950,11 @@ 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 = -EINVAL;
+		goto _badf;
+	}
+
 	group = kmalloc(sizeof(*group), GFP_KERNEL);
 	if (!group) {
 		res = -ENOMEM;
-- 
2.16.4

Re: [PATCH 4.19.y] ALSA: pcm: disallow linking stream to itself

[Greg Kroah-Hartman]

On Mon, Jun 15, 2020 at 05:41:19PM +0200, Takashi Iwai wrote:
> From: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> 
> commit 951e2736f4b11b58dc44d41964fa17c3527d882a upstream.
> 
> 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>
> Link: https://lore.kernel.org/r/89c4a2487609a0ed6af3ecf01cc972bdc59a7a2d.1591634956.git.mirq-linux@rere.qmqm.pl
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> 
> ---
> 
> Backported to 4.19.y.  It can be used for older branches, too.

Thanks, that worked.

greg k-h