From 8a56ef4f3ffba9ebf4967b61ef600b0a7ba10f11 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Thu, 19 Apr 2018 18:16:15 +0200
Subject: [PATCH] ALSA: rawmidi: Fix missing input substream checks in compat ioctls
Git-commit: 8a56ef4f3ffba9ebf4967b61ef600b0a7ba10f11
Patch-mainline: v4.17-rc2
References: bsc#1051510

Some rawmidi compat ioctls lack of the input substream checks
(although they do check only for rfile->output).  This many eventually
lead to an Oops as NULL substream is passed to the rawmidi core
functions.

Fix it by adding the proper checks before each function call.

The bug was spotted by syzkaller.

Reported-by: syzbot+f7a0348affc3b67bc617@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 sound/core/rawmidi_compat.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

--- a/sound/core/rawmidi_compat.c
+++ b/sound/core/rawmidi_compat.c
@@ -36,8 +36,6 @@ static int snd_rawmidi_ioctl_params_comp
 	struct snd_rawmidi_params params;
 	unsigned int val;
 
-	if (rfile->output == NULL)
-		return -EINVAL;
 	if (get_user(params.stream, &src->stream) ||
 	    get_user(params.buffer_size, &src->buffer_size) ||
 	    get_user(params.avail_min, &src->avail_min) ||
@@ -46,8 +44,12 @@ static int snd_rawmidi_ioctl_params_comp
 	params.no_active_sensing = val;
 	switch (params.stream) {
 	case SNDRV_RAWMIDI_STREAM_OUTPUT:
+		if (!rfile->output)
+			return -EINVAL;
 		return snd_rawmidi_output_params(rfile->output, &params);
 	case SNDRV_RAWMIDI_STREAM_INPUT:
+		if (!rfile->input)
+			return -EINVAL;
 		return snd_rawmidi_input_params(rfile->input, &params);
 	}
 	return -EINVAL;
@@ -67,16 +69,18 @@ static int snd_rawmidi_ioctl_status_comp
 	int err;
 	struct snd_rawmidi_status status;
 
-	if (rfile->output == NULL)
-		return -EINVAL;
 	if (get_user(status.stream, &src->stream))
 		return -EFAULT;
 
 	switch (status.stream) {
 	case SNDRV_RAWMIDI_STREAM_OUTPUT:
+		if (!rfile->output)
+			return -EINVAL;
 		err = snd_rawmidi_output_status(rfile->output, &status);
 		break;
 	case SNDRV_RAWMIDI_STREAM_INPUT:
+		if (!rfile->input)
+			return -EINVAL;
 		err = snd_rawmidi_input_status(rfile->input, &status);
 		break;
 	default:
@@ -112,16 +116,18 @@ static int snd_rawmidi_ioctl_status_x32(
 	int err;
 	struct snd_rawmidi_status status;
 
-	if (rfile->output == NULL)
-		return -EINVAL;
 	if (get_user(status.stream, &src->stream))
 		return -EFAULT;
 
 	switch (status.stream) {
 	case SNDRV_RAWMIDI_STREAM_OUTPUT:
+		if (!rfile->output)
+			return -EINVAL;
 		err = snd_rawmidi_output_status(rfile->output, &status);
 		break;
 	case SNDRV_RAWMIDI_STREAM_INPUT:
+		if (!rfile->input)
+			return -EINVAL;
 		err = snd_rawmidi_input_status(rfile->input, &status);
 		break;
 	default: