control: use reference-counted pid

Instead of storing the PID number, take a reference to the task's pid
structure.  This protects against duplicates due to PID overflows, and
using pid_vnr() ensures that the PID returned by snd_ctl_elem_info() is
correct as seen from the current namespace.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/control.h

@@ -86,10 +86,12 @@ struct snd_kctl_event {
 
 #define snd_kctl_event(n) list_entry(n, struct snd_kctl_event, list)
 
+struct pid;
+
 struct snd_ctl_file {
 	struct list_head list;		/* list of all control files */
 	struct snd_card *card;
-	pid_t pid;
+	struct pid *pid;
 	int prefer_pcm_subdevice;
 	int prefer_rawmidi_subdevice;
 	wait_queue_head_t change_sleep;

sound/core/control.c

@@ -75,7 +75,7 @@ static int snd_ctl_open(struct inode *inode, struct file *file)
 	ctl->card = card;
 	ctl->prefer_pcm_subdevice = -1;
 	ctl->prefer_rawmidi_subdevice = -1;
-	ctl->pid = current->pid;
+	ctl->pid = get_pid(task_pid(current));
 	file->private_data = ctl;
 	write_lock_irqsave(&card->ctl_files_rwlock, flags);
 	list_add_tail(&ctl->list, &card->ctl_files);
@@ -125,6 +125,7 @@ static int snd_ctl_release(struct inode *inode, struct file *file)
 				control->vd[idx].owner = NULL;
 	up_write(&card->controls_rwsem);
 	snd_ctl_empty_read_queue(ctl);
+	put_pid(ctl->pid);
 	kfree(ctl);
 	module_put(card->module);
 	snd_card_file_remove(card, file);
@@ -672,7 +673,7 @@ static int snd_ctl_elem_info(struct snd_ctl_file *ctl,
 			info->access |= SNDRV_CTL_ELEM_ACCESS_LOCK;
 			if (vd->owner == ctl)
 				info->access |= SNDRV_CTL_ELEM_ACCESS_OWNER;
-			info->owner = vd->owner->pid;
+			info->owner = pid_vnr(vd->owner->pid);
 		} else {
 			info->owner = -1;
 		}

sound/core/pcm.c

@@ -809,7 +809,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 	card = pcm->card;
 	read_lock(&card->ctl_files_rwlock);
 	list_for_each_entry(kctl, &card->ctl_files, list) {
-		if (kctl->pid == current->pid) {
+		if (kctl->pid == task_pid(current)) {
 			prefer_subdevice = kctl->prefer_pcm_subdevice;
 			if (prefer_subdevice != -1)
 				break;

sound/core/rawmidi.c

@@ -415,7 +415,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file)
 		subdevice = -1;
 		read_lock(&card->ctl_files_rwlock);
 		list_for_each_entry(kctl, &card->ctl_files, list) {
-			if (kctl->pid == current->pid) {
+			if (kctl->pid == task_pid(current)) {
 				subdevice = kctl->prefer_rawmidi_subdevice;
 				if (subdevice != -1)
 					break;