# \[PATCH\] video: fbdev: udlfb: Fix use after free on dlfb\_usb\_probe error path

- Subsystems: DISPLAYLINK USB 2.0 FRAMEBUFFER DRIVER (UDLFB), FRAMEBUFFER LAYER, THE REST
- Maintainers: Bernie Thompson, Helge Deller, Linus Torvalds
- List: linux-fbdev
- 2 messages, 2 authors
- Page: https://ratatoskr.run/linux-fbdev/2017/08/5065143/t

## \[PATCH\] video: fbdev: udlfb: Fix use after free on dlfb\_usb\_probe error path

- From: Anton Vasilyev \<hidden\>
- Date: 2017-08-11 12:59:10 
- Message: https://ratatoskr.run/linux-fbdev/2017/08/5065143.md

```text
If dlfb_usb_probe drops to error path then there is only one
kref_init() call and no kref_get(), so second kref_put() leads to
use after free.

The patch removes superfluous kref_put on dlfb_usb_probe error path.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Anton Vasilyev <redacted>
---
 drivers/video/fbdev/udlfb.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/video/fbdev/udlfb.c b/drivers/video/fbdev/udlfb.c
index 05ef657..f71b49f 100644
--- a/drivers/video/fbdev/udlfb.c
+++ b/drivers/video/fbdev/udlfb.c
@@ -1655,7 +1655,6 @@ static int dlfb_usb_probe(struct usb_interface *interface,
 error:
 	if (dev) {
 
-		kref_put(&dev->kref, dlfb_free); /* ref for framebuffer */
 		kref_put(&dev->kref, dlfb_free); /* last ref from kref_init */
 
 		/* dev has been deallocated. Do not dereference */
-- 
2.7.4

```

## Re: \[PATCH\] video: fbdev: udlfb: Fix use after free on dlfb\_usb\_probe error path

- From: Bartlomiej Zolnierkiewicz \<hidden\>
- Date: 2017-08-21 14:36:00 
- Message: https://ratatoskr.run/linux-fbdev/2017/08/5072170.md

```text
On Friday, August 11, 2017 03:59:01 PM Anton Vasilyev wrote:
> If dlfb_usb_probe drops to error path then there is only one
> kref_init() call and no kref_get(), so second kref_put() leads to
> use after free.
> 
> The patch removes superfluous kref_put on dlfb_usb_probe error path.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Anton Vasilyev <redacted>

Patch queued for 4.14, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

```