[PATCH] fbdev: smscufx: properly copy ioctl memory to kernelspace

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

The UFX_IOCTL_REPORT_DAMAGE ioctl does not properly copy data from
userspace to kernelspace, and instead directly references the memory,
which can cause problems if invalid data is passed from userspace.  Fix
this all up by correctly copying the memory before accessing it within
the kernel.

Reported-by: Tianchu Chen <flynnnchen@tencent.com>
Cc: stable <stable@kernel.org>
Cc: Steve Glendinning <steve.glendinning@shawell.net>
Cc: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/video/fbdev/smscufx.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
index 5f0dd01fd834..891ce7b76d63 100644
--- a/drivers/video/fbdev/smscufx.c
+++ b/drivers/video/fbdev/smscufx.c
@@ -932,7 +932,6 @@ static int ufx_ops_ioctl(struct fb_info *info, unsigned int cmd,
 			 unsigned long arg)
 {
 	struct ufx_data *dev = info->par;
-	struct dloarea *area = NULL;
 
 	if (!atomic_read(&dev->usb_active))
 		return 0;
@@ -947,6 +946,10 @@ static int ufx_ops_ioctl(struct fb_info *info, unsigned int cmd,
 
 	/* TODO: Help propose a standard fb.h ioctl to report mmap damage */
 	if (cmd == UFX_IOCTL_REPORT_DAMAGE) {
+		struct dloarea *area __free(kfree) = kmalloc(sizeof(*area), GFP_KERNEL);
+		if (!area)
+			return -ENOMEM;
+
 		/* If we have a damage-aware client, turn fb_defio "off"
 		 * To avoid perf imact of unnecessary page fault handling.
 		 * Done by resetting the delay for this fb_info to a very
@@ -956,7 +959,8 @@ static int ufx_ops_ioctl(struct fb_info *info, unsigned int cmd,
 		if (info->fbdefio)
 			info->fbdefio->delay = UFX_DEFIO_WRITE_DISABLE;
 
-		area = (struct dloarea *)arg;
+		if (copy_from_user(area, (u8 __user *)arg, sizeof(*area)))
+			return -EFAULT;
 
 		if (area->x < 0)
 			area->x = 0;
-- 
2.52.0