ALSA: seq: add an alternative way to handle ioctl requests

ALSA sequencer is designed with two types of clients; application and
kernel. Operations for each ioctl command should handle data in both of
user space and kernel space, while current implementation just allows them
to handle data in user space. Data in kernel space is handled with change
of address limit of running tasks.

This commit adds a new table to map ioctl commands to corresponding
functions. The functions get data in kernel space. Helper functions to
operate kernel and application clients seek entries from the table.
Especially, the helper function for application is responsible for coping
from user space to kernel space or vise versa.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_clientmgr.c

@@ -2168,6 +2168,13 @@ static int snd_seq_ioctl_query_next_port(struct snd_seq_client *client,
 
 /* -------------------------------------------------------- */
 
+static const struct ioctl_handler {
+	unsigned int cmd;
+	int (*func)(struct snd_seq_client *client, void *arg);
+} ioctl_handlers[] = {
+	{ 0, NULL },
+};
+
 static struct seq_ioctl_table {
 	unsigned int cmd;
 	int (*func)(struct snd_seq_client *client, void __user * arg);
@@ -2204,6 +2211,63 @@ static struct seq_ioctl_table {
 	{ 0, NULL },
 };
 
+static long seq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct snd_seq_client *client = file->private_data;
+	/* To use kernel stack for ioctl data. */
+	union ioctl_arg {
+		int pversion;
+		int client_id;
+		struct snd_seq_system_info	system_info;
+		struct snd_seq_running_info	running_info;
+		struct snd_seq_client_info	client_info;
+		struct snd_seq_port_info	port_info;
+		struct snd_seq_port_subscribe	port_subscribe;
+		struct snd_seq_queue_info	queue_info;
+		struct snd_seq_queue_status	queue_status;
+		struct snd_seq_queue_tempo	tempo;
+		struct snd_seq_queue_timer	queue_timer;
+		struct snd_seq_queue_client	queue_client;
+		struct snd_seq_client_pool	client_pool;
+		struct snd_seq_remove_events	remove_events;
+		struct snd_seq_query_subs	query_subs;
+	} buf = {0};
+	const struct ioctl_handler *handler;
+	unsigned long size;
+	int err;
+
+	if (snd_BUG_ON(!client))
+		return -ENXIO;
+
+	for (handler = ioctl_handlers; handler->cmd > 0; ++handler) {
+		if (handler->cmd == cmd)
+			break;
+	}
+	if (handler->cmd == 0)
+		return -ENOTTY;
+	/*
+	 * All of ioctl commands for ALSA sequencer get an argument of size
+	 * within 13 bits. We can safely pick up the size from the command.
+	 */
+	size = _IOC_SIZE(handler->cmd);
+	if (_IOC_DIR(handler->cmd) & IOC_IN) {
+		if (copy_from_user(&buf, (const void __user *)arg, size))
+			return -EFAULT;
+	}
+
+	err = handler->func(client, &buf);
+	if (err >= 0) {
+		/* Some commands includes a bug in 'dir' field. */
+		if (handler->cmd == SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT ||
+		    handler->cmd == SNDRV_SEQ_IOCTL_SET_CLIENT_POOL ||
+		    (_IOC_DIR(handler->cmd) & IOC_OUT))
+			if (copy_to_user((void __user *)arg, &buf, size))
+				return -EFAULT;
+	}
+
+	return err;
+}
+
 static int snd_seq_do_ioctl(struct snd_seq_client *client, unsigned int cmd,
 			    void __user *arg)
 {
@@ -2234,6 +2298,9 @@ static long snd_seq_ioctl(struct file *file, unsigned int cmd, unsigned long arg
 {
 	struct snd_seq_client *client = file->private_data;
 
+	if (seq_ioctl(file, cmd, arg) >= 0)
+		return 0;
+
 	if (snd_BUG_ON(!client))
 		return -ENXIO;
 
@@ -2437,6 +2504,7 @@ EXPORT_SYMBOL(snd_seq_kernel_client_dispatch);
  */
 int snd_seq_kernel_client_ctl(int clientid, unsigned int cmd, void *arg)
 {
+	const struct ioctl_handler *handler;
 	struct snd_seq_client *client;
 	mm_segment_t fs;
 	int result;
@@ -2444,6 +2512,12 @@ int snd_seq_kernel_client_ctl(int clientid, unsigned int cmd, void *arg)
 	client = clientptr(clientid);
 	if (client == NULL)
 		return -ENXIO;
+
+	for (handler = ioctl_handlers; handler->cmd > 0; ++handler) {
+		if (handler->cmd == cmd)
+			return handler->func(client, arg);
+	}
+
 	fs = snd_enter_user();
 	result = snd_seq_do_ioctl(client, cmd, (void __force __user *)arg);
 	snd_leave_user(fs);

sound/core/seq/seq_compat.c

@@ -59,6 +59,9 @@ static int snd_seq_call_port_info_ioctl(struct snd_seq_client *client, unsigned
 		goto error;
 	data->kernel = NULL;
 
+	if (snd_seq_kernel_client_ctl(client->number, cmd, &data) >= 0)
+		return 0;
+
 	fs = snd_enter_user();
 	err = snd_seq_do_ioctl(client, cmd, data);
 	snd_leave_user(fs);
@@ -123,6 +126,8 @@ static long snd_seq_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 	case SNDRV_SEQ_IOCTL_GET_SUBSCRIPTION:
 	case SNDRV_SEQ_IOCTL_QUERY_NEXT_CLIENT:
 	case SNDRV_SEQ_IOCTL_RUNNING_MODE:
+		if (seq_ioctl(file, cmd, arg) >= 0)
+			return 0;
 		return snd_seq_do_ioctl(client, cmd, argp);
 	case SNDRV_SEQ_IOCTL_CREATE_PORT32:
 		return snd_seq_call_port_info_ioctl(client, SNDRV_SEQ_IOCTL_CREATE_PORT, argp);