[ALSA] Fix races in PCM OSS emulation

Fixed the race among multiple threads accessing the OSS PCM
instance concurrently by simply introducing a mutex for protecting
a setup of the PCM.

Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Jaroslav Kysela <[e-mail]>

include/sound/pcm_oss.h

···
 	size_t mmap_bytes;
 	char *buffer;				/* vmallocated period */
 	size_t buffer_used;			/* used length from period buffer */
+	struct mutex params_lock;
 #ifdef CONFIG_SND_PCM_OSS_PLUGINS
 	struct snd_pcm_plugin *plugin_first;
 	struct snd_pcm_plugin *plugin_last;

sound/core/oss/pcm_oss.c

···
 	struct snd_mask sformat_mask;
 	struct snd_mask mask;
 
+	if (mutex_lock_interruptible(&runtime->oss.params_lock))
+		return -EINTR;
 	sw_params = kmalloc(sizeof(*sw_params), GFP_KERNEL);
 	params = kmalloc(sizeof(*params), GFP_KERNEL);
 	sparams = kmalloc(sizeof(*sparams), GFP_KERNEL);
···
 	kfree(sw_params);
 	kfree(params);
 	kfree(sparams);
+	mutex_unlock(&runtime->oss.params_lock);
 	return err;
 }
 
···
 
 	if ((tmp = snd_pcm_oss_make_ready(substream)) < 0)
 		return tmp;
+	mutex_lock(&runtime->oss.params_lock);
 	while (bytes > 0) {
 		if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) {
 			tmp = bytes;
 			if (tmp + runtime->oss.buffer_used > runtime->oss.period_bytes)
 				tmp = runtime->oss.period_bytes - runtime->oss.buffer_used;
 			if (tmp > 0) {
-				if (copy_from_user(runtime->oss.buffer + runtime->oss.buffer_used, buf, tmp))
-					return xfer > 0 ? (snd_pcm_sframes_t)xfer : -EFAULT;
+				if (copy_from_user(runtime->oss.buffer + runtime->oss.buffer_used, buf, tmp)) {
+					tmp = -EFAULT;
+					goto err;
+				}
 			}
 			runtime->oss.buffer_used += tmp;
 			buf += tmp;
···
 				tmp = snd_pcm_oss_write2(substream, runtime->oss.buffer + runtime->oss.period_ptr, 
 							 runtime->oss.buffer_used - runtime->oss.period_ptr, 1);
 				if (tmp <= 0)
-					return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
+					goto err;
 				runtime->oss.bytes += tmp;
 				runtime->oss.period_ptr += tmp;
 				runtime->oss.period_ptr %= runtime->oss.period_bytes;
 				if (runtime->oss.period_ptr == 0 ||
 				    runtime->oss.period_ptr == runtime->oss.buffer_used)
 					runtime->oss.buffer_used = 0;
-				else if ((substream->f_flags & O_NONBLOCK) != 0)
-					return xfer > 0 ? xfer : -EAGAIN;
+				else if ((substream->f_flags & O_NONBLOCK) != 0) {
+					tmp = -EAGAIN;
+					goto err;
+				}
 			}
 		} else {
 			tmp = snd_pcm_oss_write2(substream,
 						 (const char __force *)buf,
 						 runtime->oss.period_bytes, 0);
 			if (tmp <= 0)
-				return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
+				goto err;
 			runtime->oss.bytes += tmp;
 			buf += tmp;
 			bytes -= tmp;
···
 				break;
 		}
 	}
+	mutex_unlock(&runtime->oss.params_lock);
 	return xfer;
+
+ err:
+	mutex_unlock(&runtime->oss.params_lock);
+	return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
 }
 
 static ssize_t snd_pcm_oss_read2(struct snd_pcm_substream *substream, char *buf, size_t bytes, int in_kernel)
···
 
 	if ((tmp = snd_pcm_oss_make_ready(substream)) < 0)
 		return tmp;
+	mutex_lock(&runtime->oss.params_lock);
 	while (bytes > 0) {
 		if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) {
 			if (runtime->oss.buffer_used == 0) {
 				tmp = snd_pcm_oss_read2(substream, runtime->oss.buffer, runtime->oss.period_bytes, 1);
 				if (tmp <= 0)
-					return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
+					goto err;
 				runtime->oss.bytes += tmp;
 				runtime->oss.period_ptr = tmp;
 				runtime->oss.buffer_used = tmp;
···
 			tmp = bytes;
 			if ((size_t) tmp > runtime->oss.buffer_used)
 				tmp = runtime->oss.buffer_used;
-			if (copy_to_user(buf, runtime->oss.buffer + (runtime->oss.period_ptr - runtime->oss.buffer_used), tmp))
-				return xfer > 0 ? (snd_pcm_sframes_t)xfer : -EFAULT;
+			if (copy_to_user(buf, runtime->oss.buffer + (runtime->oss.period_ptr - runtime->oss.buffer_used), tmp)) {
+				tmp = -EFAULT;
+				goto err;
+			}
 			buf += tmp;
 			bytes -= tmp;
 			xfer += tmp;
···
 			tmp = snd_pcm_oss_read2(substream, (char __force *)buf,
 						runtime->oss.period_bytes, 0);
 			if (tmp <= 0)
-				return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
+				goto err;
 			runtime->oss.bytes += tmp;
 			buf += tmp;
 			bytes -= tmp;
 			xfer += tmp;
 		}
 	}
+	mutex_unlock(&runtime->oss.params_lock);
 	return xfer;
+
+ err:
+	mutex_unlock(&runtime->oss.params_lock);
+	return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
 }
 
 static int snd_pcm_oss_reset(struct snd_pcm_oss_file *pcm_oss_file)
···
 			return err;
 		format = snd_pcm_oss_format_from(runtime->oss.format);
 		width = snd_pcm_format_physical_width(format);
+		mutex_lock(&runtime->oss.params_lock);
 		if (runtime->oss.buffer_used > 0) {
 #ifdef OSS_DEBUG
 			printk("sync: buffer_used\n");
···
 						   runtime->oss.buffer + runtime->oss.buffer_used,
 						   size);
 			err = snd_pcm_oss_sync1(substream, runtime->oss.period_bytes);
-			if (err < 0)
+			if (err < 0) {
+				mutex_unlock(&runtime->oss.params_lock);
 				return err;
+			}
 		} else if (runtime->oss.period_ptr > 0) {
 #ifdef OSS_DEBUG
 			printk("sync: period_ptr\n");
···
 						   runtime->oss.buffer,
 						   size * 8 / width);
 			err = snd_pcm_oss_sync1(substream, size);
-			if (err < 0)
+			if (err < 0) {
+				mutex_unlock(&runtime->oss.params_lock);
 				return err;
+			}
 		}
 		/*
 		 * The ALSA's period might be a bit large than OSS one.
···
 				snd_pcm_lib_writev(substream, buffers, size);
 			}
 		}
+		mutex_unlock(&runtime->oss.params_lock);
 		/*
 		 * finish sync: drain the buffer
 		 */
···
 	runtime->oss.params = 1;
 	runtime->oss.trigger = 1;
 	runtime->oss.rate = 8000;
+	mutex_init(&runtime->oss.params_lock);
 	switch (SNDRV_MINOR_OSS_DEVICE(minor)) {
 	case SNDRV_MINOR_OSS_PCM_8:
 		runtime->oss.format = AFMT_U8;