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>

1 files changed, 63 insertions, 10 deletions

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 1657b9608b04..2cd500a304f2 100644
--- a/drivers/video/console/fbcon.c
+++ b/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++) {
@@ -3124,7 +3132,7 @@ static void fbcon_get_requirement(struct fb_info *info,
         }
 }
 
-static int fbcon_event_notify(struct notifier_block *self, 
+static int fbcon_event_notify(struct notifier_block *self,
                               unsigned long action, void *data)
 {
         struct fb_event *event = data;
@@ -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;
 }