fbmem: don't call copy_from/to_user() with mutex held

Avoid calling copy_from/to_user() with fb_info->lock mutex held in fbmem
ioctl().

fb_mmap() is called under mm->mmap_sem (A) held, that also acquires
fb_info->lock (B); fb_ioctl() takes fb_info->lock (B) and does
copy_from/to_user() that might acquire mm->mmap_sem (A), causing a
deadlock.

NOTE: it doesn't push down the fb_info->lock in each own driver's
fb_ioctl(), so there are still potential deadlocks elsewhere.

Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Johannes Weiner <hannes@saeurebad.de>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 69 insertions, 66 deletions

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 756efeb91ab..cfd9dce1ce0 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1013,132 +1013,139 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 	struct fb_var_screeninfo var;
 	struct fb_fix_screeninfo fix;
 	struct fb_con2fbmap con2fb;
+	struct fb_cmap cmap_from;
 	struct fb_cmap_user cmap;
 	struct fb_event event;
 	void __user *argp = (void __user *)arg;
 	long ret = 0;
 
-	fb = info->fbops;
-	if (!fb)
-		return -ENODEV;
-
 	switch (cmd) {
 	case FBIOGET_VSCREENINFO:
-		ret = copy_to_user(argp, &info->var,
-				    sizeof(var)) ? -EFAULT : 0;
+		if (!lock_fb_info(info))
+			return -ENODEV;
+		var = info->var;
+		unlock_fb_info(info);
+
+		ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;
 		break;
 	case FBIOPUT_VSCREENINFO:
-		if (copy_from_user(&var, argp, sizeof(var))) {
-			ret =  -EFAULT;
-			break;
-		}
+		if (copy_from_user(&var, argp, sizeof(var)))
+			return -EFAULT;
+		if (!lock_fb_info(info))
+			return -ENODEV;
 		acquire_console_sem();
 		info->flags |= FBINFO_MISC_USEREVENT;
 		ret = fb_set_var(info, &var);
 		info->flags &= ~FBINFO_MISC_USEREVENT;
 		release_console_sem();
-		if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
+		unlock_fb_info(info);
+		if (!ret && copy_to_user(argp, &var, sizeof(var)))
 			ret = -EFAULT;
 		break;
 	case FBIOGET_FSCREENINFO:
-		ret = copy_to_user(argp, &info->fix,
-				    sizeof(fix)) ? -EFAULT : 0;
+		if (!lock_fb_info(info))
+			return -ENODEV;
+		fix = info->fix;
+		unlock_fb_info(info);
+
+		ret = copy_to_user(argp, &fix, sizeof(fix)) ? -EFAULT : 0;
 		break;
 	case FBIOPUTCMAP:
 		if (copy_from_user(&cmap, argp, sizeof(cmap)))
-			ret = -EFAULT;
-		else
-			ret = fb_set_user_cmap(&cmap, info);
+			return -EFAULT;
+		ret = fb_set_user_cmap(&cmap, info);
 		break;
 	case FBIOGETCMAP:
 		if (copy_from_user(&cmap, argp, sizeof(cmap)))
-			ret = -EFAULT;
-		else
-			ret = fb_cmap_to_user(&info->cmap, &cmap);
+			return -EFAULT;
+		if (!lock_fb_info(info))
+			return -ENODEV;
+		cmap_from = info->cmap;
+		unlock_fb_info(info);
+		ret = fb_cmap_to_user(&cmap_from, &cmap);
 		break;
 	case FBIOPAN_DISPLAY:
-		if (copy_from_user(&var, argp, sizeof(var))) {
-			ret = -EFAULT;
-			break;
-		}
+		if (copy_from_user(&var, argp, sizeof(var)))
+			return -EFAULT;
+		if (!lock_fb_info(info))
+			return -ENODEV;
 		acquire_console_sem();
 		ret = fb_pan_display(info, &var);
 		release_console_sem();
+		unlock_fb_info(info);
 		if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
-			ret = -EFAULT;
+			return -EFAULT;
 		break;
 	case FBIO_CURSOR:
 		ret = -EINVAL;
 		break;
 	case FBIOGET_CON2FBMAP:
 		if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
-			ret = -EFAULT;
-		else if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
-			ret = -EINVAL;
-		else {
-			con2fb.framebuffer = -1;
-			event.info = info;
-			event.data = &con2fb;
-			fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP,
-								&event);
-			ret = copy_to_user(argp, &con2fb,
-				    sizeof(con2fb)) ? -EFAULT : 0;
-		}
+			return -EFAULT;
+		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
+			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:
-		if (copy_from_user(&con2fb, argp, sizeof(con2fb))) {
-			ret = -EFAULT;
-			break;
-		}
-		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES) {
-			ret = -EINVAL;
-			break;
-		}
-		if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX) {
-			ret = -EINVAL;
-			break;
-		}
+		if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
+			return -EFAULT;
+		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
+			return -EINVAL;
+		if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
+			return -EINVAL;
 		if (!registered_fb[con2fb.framebuffer])
 			request_module("fb%d", con2fb.framebuffer);
 		if (!registered_fb[con2fb.framebuffer]) {
 			ret = -EINVAL;
 			break;
 		}
-		event.info = info;
 		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);
 		break;
 	case FBIOBLANK:
+		if (!lock_fb_info(info))
+			return -ENODEV;
 		acquire_console_sem();
 		info->flags |= FBINFO_MISC_USEREVENT;
 		ret = fb_blank(info, arg);
 		info->flags &= ~FBINFO_MISC_USEREVENT;
 		release_console_sem();
-		break;;
+		unlock_fb_info(info);
+		break;
 	default:
-		if (fb->fb_ioctl == NULL)
-			ret = -ENOTTY;
-		else
+		if (!lock_fb_info(info))
+			return -ENODEV;
+		fb = info->fbops;
+		if (fb->fb_ioctl)
 			ret = fb->fb_ioctl(info, cmd, arg);
+		else
+			ret = -ENOTTY;
+		unlock_fb_info(info);
 	}
 	return ret;
 }
 
 static long fb_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
-__acquires(&info->lock)
-__releases(&info->lock)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	int fbidx = iminor(inode);
-	struct fb_info *info;
-	long ret;
+	struct fb_info *info = registered_fb[fbidx];
 
-	info = registered_fb[fbidx];
-	mutex_lock(&info->lock);
-	ret = do_fb_ioctl(info, cmd, arg);
-	mutex_unlock(&info->lock);
-	return ret;
+	return do_fb_ioctl(info, cmd, arg);
 }
 
 #ifdef CONFIG_COMPAT
@@ -1257,8 +1264,6 @@ static int fb_get_fscreeninfo(struct fb_info *info, unsigned int cmd,
 
 static long fb_compat_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg)
-__acquires(&info->lock)
-__releases(&info->lock)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	int fbidx = iminor(inode);
@@ -1266,7 +1271,6 @@ __releases(&info->lock)
 	struct fb_ops *fb = info->fbops;
 	long ret = -ENOIOCTLCMD;
 
-	mutex_lock(&info->lock);
 	switch(cmd) {
 	case FBIOGET_VSCREENINFO:
 	case FBIOPUT_VSCREENINFO:
@@ -1292,7 +1296,6 @@ __releases(&info->lock)
 			ret = fb->fb_compat_ioctl(info, cmd, arg);
 		break;
 	}
-	mutex_unlock(&info->lock);
 	return ret;
 }
 #endif