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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Takashi Iwai <tiwai@suse.de>
Subject: [PATCH 4.4 68/97] ALSA: pcm: Return -EBUSY for OSS ioctls changing busy streams
Date:   Sun, 22 Apr 2018 15:53:46 +0200
Message-Id: <20180422135308.991252429@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Takashi Iwai <tiwai@suse.de>

commit 40cab6e88cb0b6c56d3f30b7491a20e803f948f6 upstream.

OSS PCM stream management isn't modal but it allows ioctls issued at
any time for changing the parameters.  In the previous hardening
patch ("ALSA: pcm: Avoid potential races between OSS ioctls and
read/write"), we covered these races and prevent the corruption by
protecting the concurrent accesses via params_lock mutex.  However,
this means that some ioctls that try to change the stream parameter
(e.g. channels or format) would be blocked until the read/write
finishes, and it may take really long.

Basically changing the parameter while reading/writing is an invalid
operation, hence it's even more user-friendly from the API POV if it
returns -EBUSY in such a situation.

This patch adds such checks in the relevant ioctls with the addition
of read/write access refcount.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/sound/pcm_oss.h  |    1 +
 sound/core/oss/pcm_oss.c |   36 +++++++++++++++++++++++++++---------
 2 files changed, 28 insertions(+), 9 deletions(-)

--- a/include/sound/pcm_oss.h
+++ b/include/sound/pcm_oss.h
@@ -57,6 +57,7 @@ struct snd_pcm_oss_runtime {
 	char *buffer;				/* vmallocated period */
 	size_t buffer_used;			/* used length from period buffer */
 	struct mutex params_lock;
+	atomic_t rw_ref;		/* concurrent read/write accesses */
 #ifdef CONFIG_SND_PCM_OSS_PLUGINS
 	struct snd_pcm_plugin *plugin_first;
 	struct snd_pcm_plugin *plugin_last;
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1404,6 +1404,7 @@ static ssize_t snd_pcm_oss_write1(struct
 	if (atomic_read(&substream->mmap_count))
 		return -ENXIO;
 
+	atomic_inc(&runtime->oss.rw_ref);
 	while (bytes > 0) {
 		if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
 			tmp = -ERESTARTSYS;
@@ -1467,6 +1468,7 @@ static ssize_t snd_pcm_oss_write1(struct
 		}
 		tmp = 0;
 	}
+	atomic_dec(&runtime->oss.rw_ref);
 	return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
 }
 
@@ -1512,6 +1514,7 @@ static ssize_t snd_pcm_oss_read1(struct
 	if (atomic_read(&substream->mmap_count))
 		return -ENXIO;
 
+	atomic_inc(&runtime->oss.rw_ref);
 	while (bytes > 0) {
 		if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
 			tmp = -ERESTARTSYS;
@@ -1560,6 +1563,7 @@ static ssize_t snd_pcm_oss_read1(struct
 		}
 		tmp = 0;
 	}
+	atomic_dec(&runtime->oss.rw_ref);
 	return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
 }
 
@@ -1666,8 +1670,11 @@ static int snd_pcm_oss_sync(struct snd_p
 			goto __direct;
 		if ((err = snd_pcm_oss_make_ready(substream)) < 0)
 			return err;
-		if (mutex_lock_interruptible(&runtime->oss.params_lock))
+		atomic_inc(&runtime->oss.rw_ref);
+		if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
+			atomic_dec(&runtime->oss.rw_ref);
 			return -ERESTARTSYS;
+		}
 		format = snd_pcm_oss_format_from(runtime->oss.format);
 		width = snd_pcm_format_physical_width(format);
 		if (runtime->oss.buffer_used > 0) {
@@ -1679,10 +1686,8 @@ static int snd_pcm_oss_sync(struct snd_p
 						   runtime->oss.buffer + runtime->oss.buffer_used,
 						   size);
 			err = snd_pcm_oss_sync1(substream, runtime->oss.period_bytes);
-			if (err < 0) {
-				mutex_unlock(&runtime->oss.params_lock);
-				return err;
-			}
+			if (err < 0)
+				goto unlock;
 		} else if (runtime->oss.period_ptr > 0) {
 #ifdef OSS_DEBUG
 			pcm_dbg(substream->pcm, "sync: period_ptr\n");
@@ -1692,10 +1697,8 @@ static int snd_pcm_oss_sync(struct snd_p
 						   runtime->oss.buffer,
 						   size * 8 / width);
 			err = snd_pcm_oss_sync1(substream, size);
-			if (err < 0) {
-				mutex_unlock(&runtime->oss.params_lock);
-				return err;
-			}
+			if (err < 0)
+				goto unlock;
 		}
 		/*
 		 * The ALSA's period might be a bit large than OSS one.
@@ -1726,7 +1729,11 @@ static int snd_pcm_oss_sync(struct snd_p
 				snd_pcm_lib_writev(substream, buffers, size);
 			}
 		}
+unlock:
 		mutex_unlock(&runtime->oss.params_lock);
+		atomic_dec(&runtime->oss.rw_ref);
+		if (err < 0)
+			return err;
 		/*
 		 * finish sync: drain the buffer
 		 */
@@ -1774,6 +1781,8 @@ static int snd_pcm_oss_set_rate(struct s
 			rate = 192000;
 		if (mutex_lock_interruptible(&runtime->oss.params_lock))
 			return -ERESTARTSYS;
+		if (atomic_read(&runtime->oss.rw_ref))
+			return -EBUSY;
 		if (runtime->oss.rate != rate) {
 			runtime->oss.params = 1;
 			runtime->oss.rate = rate;
@@ -1808,6 +1817,8 @@ static int snd_pcm_oss_set_channels(stru
 		runtime = substream->runtime;
 		if (mutex_lock_interruptible(&runtime->oss.params_lock))
 			return -ERESTARTSYS;
+		if (atomic_read(&runtime->oss.rw_ref))
+			return -EBUSY;
 		if (runtime->oss.channels != channels) {
 			runtime->oss.params = 1;
 			runtime->oss.channels = channels;
@@ -1898,6 +1909,8 @@ static int snd_pcm_oss_set_format(struct
 			if (substream == NULL)
 				continue;
 			runtime = substream->runtime;
+			if (atomic_read(&runtime->oss.rw_ref))
+				return -EBUSY;
 			if (mutex_lock_interruptible(&runtime->oss.params_lock))
 				return -ERESTARTSYS;
 			if (runtime->oss.format != format) {
@@ -1952,6 +1965,8 @@ static int snd_pcm_oss_set_subdivide(str
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
+		if (atomic_read(&runtime->oss.rw_ref))
+			return -EBUSY;
 		if (mutex_lock_interruptible(&runtime->oss.params_lock))
 			return -ERESTARTSYS;
 		err = snd_pcm_oss_set_subdivide1(substream, subdivide);
@@ -1990,6 +2005,8 @@ static int snd_pcm_oss_set_fragment(stru
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
+		if (atomic_read(&runtime->oss.rw_ref))
+			return -EBUSY;
 		if (mutex_lock_interruptible(&runtime->oss.params_lock))
 			return -ERESTARTSYS;
 		err = snd_pcm_oss_set_fragment1(substream, val);
@@ -2384,6 +2401,7 @@ static void snd_pcm_oss_init_substream(s
 	runtime->oss.maxfrags = 0;
 	runtime->oss.subdivision = 0;
 	substream->pcm_release = snd_pcm_oss_release_substream;
+	atomic_set(&runtime->oss.rw_ref, 0);
 }
 
 static int snd_pcm_oss_release_file(struct snd_pcm_oss_file *pcm_oss_file)