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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        syzbot+6f11c7e2a1b91d466432@syzkaller.appspotmail.com,
        "Takashi Iwai" <tiwai@suse.de>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
Message-ID: <lsq.1519831218.852109083@decadent.org.uk>
Subject: [PATCH 3.16 155/254] ALSA: pcm: Remove incorrect snd_BUG_ON() usages
In-Reply-To: <lsq.1519831217.271785318@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

commit fe08f34d066f4404934a509b6806db1a4f700c86 upstream.

syzkaller triggered kernel warnings through PCM OSS emulation at
closing a stream:
  WARNING: CPU: 0 PID: 3502 at sound/core/pcm_lib.c:1635
  snd_pcm_hw_param_first+0x289/0x690 sound/core/pcm_lib.c:1635
  Call Trace:
  ....
   snd_pcm_hw_param_near.constprop.27+0x78d/0x9a0 sound/core/oss/pcm_oss.c:457
   snd_pcm_oss_change_params+0x17d3/0x3720 sound/core/oss/pcm_oss.c:969
   snd_pcm_oss_make_ready+0xaa/0x130 sound/core/oss/pcm_oss.c:1128
   snd_pcm_oss_sync+0x257/0x830 sound/core/oss/pcm_oss.c:1638
   snd_pcm_oss_release+0x20b/0x280 sound/core/oss/pcm_oss.c:2431
   __fput+0x327/0x7e0 fs/file_table.c:210
   ....

This happens while it tries to open and set up the aloop device
concurrently.  The warning above (invoked from snd_BUG_ON() macro) is
to detect the unexpected logical error where snd_pcm_hw_refine() call
shouldn't fail.  The theory is true for the case where the hw_params
config rules are static.  But for an aloop device, the hw_params rule
condition does vary dynamically depending on the connected target;
when another device is opened and changes the parameters, the device
connected in another side is also affected, and it caused the error
from snd_pcm_hw_refine().

That is, the simplest "solution" for this is to remove the incorrect
assumption of static rules, and treat such an error as a normal error
path.  As there are a couple of other places using snd_BUG_ON()
incorrectly, this patch removes these spurious snd_BUG_ON() calls.

Reported-by: syzbot+6f11c7e2a1b91d466432@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 sound/core/oss/pcm_oss.c | 1 -
 sound/core/pcm_lib.c     | 4 ++--
 2 files changed, 2 insertions(+), 3 deletions(-)

--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -465,7 +465,6 @@ static int snd_pcm_hw_param_near(struct
 		v = snd_pcm_hw_param_last(pcm, params, var, dir);
 	else
 		v = snd_pcm_hw_param_first(pcm, params, var, dir);
-	snd_BUG_ON(v < 0);
 	return v;
 }
 
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1631,7 +1631,7 @@ int snd_pcm_hw_param_first(struct snd_pc
 		return changed;
 	if (params->rmask) {
 		int err = snd_pcm_hw_refine(pcm, params);
-		if (snd_BUG_ON(err < 0))
+		if (err < 0)
 			return err;
 	}
 	return snd_pcm_hw_param_value(params, var, dir);
@@ -1678,7 +1678,7 @@ int snd_pcm_hw_param_last(struct snd_pcm
 		return changed;
 	if (params->rmask) {
 		int err = snd_pcm_hw_refine(pcm, params);
-		if (snd_BUG_ON(err < 0))
+		if (err < 0)
 			return err;
 	}
 	return snd_pcm_hw_param_value(params, var, dir);