fbmem: fix fb_info->lock and mm->mmap_sem circular locking dependency

Fix a circular locking dependency in the frame buffer console driver
pushing down the mutex fb_info->lock.

Circular locking dependecies occur calling the blocking
fb_notifier_call_chain() with fb_info->lock held.  Notifier callbacks can
try to acquire mm->mmap_sem, while fb_mmap() acquires the locks in the
reverse order mm->mmap_sem => fb_info->lock.
Tested-by: Andrey Borzenkov <arvidjaar@mail.ru>
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/backlight.c

@@ -35,6 +35,8 @@ static int fb_notifier_callback(struct notifier_block *self,
 		return 0;
 
 	bd = container_of(self, struct backlight_device, fb_notif);
+	if (!lock_fb_info(evdata->info))
+		return -ENODEV;
 	mutex_lock(&bd->ops_lock);
 	if (bd->ops)
 		if (!bd->ops->check_fb ||
@@ -47,6 +49,7 @@ static int fb_notifier_callback(struct notifier_block *self,
 			backlight_update_status(bd);
 		}
 	mutex_unlock(&bd->ops_lock);
+	unlock_fb_info(evdata->info);
 	return 0;
 }
 

drivers/video/backlight/lcd.c

@@ -40,6 +40,8 @@ static int fb_notifier_callback(struct notifier_block *self,
 	if (!ld->ops)
 		return 0;
 
+	if (!lock_fb_info(evdata->info))
+		return -ENODEV;
 	mutex_lock(&ld->ops_lock);
 	if (!ld->ops->check_fb || ld->ops->check_fb(ld, evdata->info)) {
 		if (event == FB_EVENT_BLANK) {
@@ -51,6 +53,7 @@ static int fb_notifier_callback(struct notifier_block *self,
 		}
 	}
 	mutex_unlock(&ld->ops_lock);
+	unlock_fb_info(evdata->info);
 	return 0;
 }
 

drivers/video/console/fbcon.c

@@ -2954,8 +2954,11 @@ static int fbcon_fb_unbind(int idx)
 
 static int fbcon_fb_unregistered(struct fb_info *info)
 {
-	int i, idx = info->node;
+	int i, idx;
 
+	if (!lock_fb_info(info))
+		return -ENODEV;
+	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] == idx)
 			con2fb_map[i] = -1;
@@ -2979,13 +2982,14 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 		}
 	}
 
-	if (!num_registered_fb)
-		unregister_con_driver(&fb_con);
-
-
 	if (primary_device == idx)
 		primary_device = -1;
 
+	unlock_fb_info(info);
+
+	if (!num_registered_fb)
+		unregister_con_driver(&fb_con);
+
 	return 0;
 }
 
@@ -3021,9 +3025,13 @@ static inline void fbcon_select_primary(struct fb_info *info)
 
 static int fbcon_fb_registered(struct fb_info *info)
 {
-	int ret = 0, i, idx = info->node;
+	int ret = 0, i, idx;
 
+	if (!lock_fb_info(info))
+		return -ENODEV;
+	idx = info->node;
 	fbcon_select_primary(info);
+	unlock_fb_info(info);
 
 	if (info_idx == -1) {
 		for (i = first_fb_vc; i <= last_fb_vc; i++) {
@@ -3132,7 +3140,7 @@ static int fbcon_event_notify(struct notifier_block *self,
 	struct fb_videomode *mode;
 	struct fb_con2fbmap *con2fb;
 	struct fb_blit_caps *caps;
-	int ret = 0;
+	int idx, ret = 0;
 
 	/*
 	 * ignore all events except driver registration and deregistration
@@ -3144,23 +3152,54 @@ static int fbcon_event_notify(struct notifier_block *self,
 
 	switch(action) {
 	case FB_EVENT_SUSPEND:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_suspended(info);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_RESUME:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_resumed(info);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_MODE_CHANGE:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_modechanged(info);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_MODE_CHANGE_ALL:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_set_all_vcs(info);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_MODE_DELETE:
 		mode = event->data;
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		ret = fbcon_mode_deleted(info, mode);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_FB_UNBIND:
-		ret = fbcon_fb_unbind(info->node);
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
+		idx = info->node;
+		unlock_fb_info(info);
+		ret = fbcon_fb_unbind(idx);
 		break;
 	case FB_EVENT_FB_REGISTERED:
 		ret = fbcon_fb_registered(info);
@@ -3178,17 +3217,31 @@ static int fbcon_event_notify(struct notifier_block *self,
 		con2fb->framebuffer = con2fb_map[con2fb->console - 1];
 		break;
 	case FB_EVENT_BLANK:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_fb_blanked(info, *(int *)event->data);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_NEW_MODELIST:
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_new_modelist(info);
+		unlock_fb_info(info);
 		break;
 	case FB_EVENT_GET_REQ:
 		caps = event->data;
+		if (!lock_fb_info(info)) {
+			ret = -ENODEV;
+			goto done;
+		}
 		fbcon_get_requirement(info, caps);
+		unlock_fb_info(info);
 		break;
 	}
-
 done:
 	return ret;
 }

drivers/video/fbmem.c

@@ -1086,13 +1086,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 			return -EINVAL;
 		con2fb.framebuffer = -1;
 		event.data = &con2fb;
-
-		if (!lock_fb_info(info))
-			return -ENODEV;
 		event.info = info;
 		fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
-		unlock_fb_info(info);
-
 		ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
 		break;
 	case FBIOPUT_CON2FBMAP:
@@ -1109,12 +1104,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 			break;
 		}
 		event.data = &con2fb;
-		if (!lock_fb_info(info))
-			return -ENODEV;
 		event.info = info;
-		ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP,
-					      &event);
-		unlock_fb_info(info);
+		ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
 		break;
 	case FBIOBLANK:
 		if (!lock_fb_info(info))