From 951e2736f4b11b58dc44d41964fa17c3527d882a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20Miros=C5=82aw?= <mirq-linux@rere.qmqm.pl>
Date: Mon, 8 Jun 2020 18:50:39 +0200
Subject: [PATCH] ALSA: pcm: disallow linking stream to itself
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Git-commit: 951e2736f4b11b58dc44d41964fa17c3527d882a
Patch-mainline: v5.8-rc1
References: bsc#1111666

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>

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

--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1986,6 +1986,11 @@ static int snd_pcm_link(struct snd_pcm_s
 	}
 	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;