[PATCH v2 RESEND] media: as102: fix to not free memory after the device is registered in as102_usb_probe()
In as102_usb driver, the following race condition occurs: ``` CPU0 CPU1 as102_usb_probe() kzalloc(); // alloc as102_dev_t .... usb_register_dev(); open("/path/to/dev"); // open as102 dev .... usb_deregister_dev(); .... kfree(); // free as102_dev_t .... close(fd); as102_release() // UAF!! as102_usb_release() kfree(); // DFB!! ```
When a USB character device registered with usb_register_dev() is later unregistered (via usb_deregister_dev() or disconnect), the device node is removed so new open() calls fail. However, file descriptors that are already open do not go away immediately: they remain valid until the last reference is dropped and the driver's .release() is invoked.
In as102, as102_usb_probe() calls usb_register_dev() and then, on an error path, does usb_deregister_dev() and frees as102_dev_t right away. If userspace raced a successful open() before the deregistration, that open FD will later hit as102_release() --> as102_usb_release() and access or free as102_dev_t again, occur a race to use-after-free and double-free vuln.
The fix is to never kfree(as102_dev_t) directly once usb_register_dev() has succeeded. After deregistration, defer freeing memory to .release().
In other words, let release() perform the last kfree when the final open FD is closed.
Cc: stable@vger.kernel.org Reported-by: syzbot+47321e8fd5a4c84088db@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=47321e8fd5a4c84088db Fixes: cd19f7d3e39b ("[media] as102: fix leaks at failure paths in as102_usb_probe()") Signed-off-by: Jeongjun Park aha310510@gmail.com --- v2: Fix incorrect patch description style and CC stable mailing list - Link to v1: https://lore.kernel.org/all/20250822143539.1157329-1-aha310510@gmail.com/ --- drivers/media/usb/as102/as102_usb_drv.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/media/usb/as102/as102_usb_drv.c b/drivers/media/usb/as102/as102_usb_drv.c index e0ef66a522e2..abde5666b2ee 100644 --- a/drivers/media/usb/as102/as102_usb_drv.c +++ b/drivers/media/usb/as102/as102_usb_drv.c @@ -404,6 +404,7 @@ static int as102_usb_probe(struct usb_interface *intf, as102_free_usb_stream_buffer(as102_dev); failed_stream: usb_deregister_dev(intf, &as102_usb_class_driver); + return ret; failed: usb_put_dev(as102_dev->bus_adap.usb_dev); usb_set_intfdata(intf, NULL); --
On 04/09/2025 07:46, Jeongjun Park wrote:
In as102_usb driver, the following race condition occurs:
CPU0 CPU1 as102_usb_probe() kzalloc(); // alloc as102_dev_t .... usb_register_dev(); open("/path/to/dev"); // open as102 dev .... usb_deregister_dev(); .... kfree(); // free as102_dev_t .... close(fd); as102_release() // UAF!! as102_usb_release() kfree(); // DFB!!When a USB character device registered with usb_register_dev() is later unregistered (via usb_deregister_dev() or disconnect), the device node is removed so new open() calls fail. However, file descriptors that are already open do not go away immediately: they remain valid until the last reference is dropped and the driver's .release() is invoked.
In as102, as102_usb_probe() calls usb_register_dev() and then, on an error path, does usb_deregister_dev() and frees as102_dev_t right away. If userspace raced a successful open() before the deregistration, that open FD will later hit as102_release() --> as102_usb_release() and access or free as102_dev_t again, occur a race to use-after-free and double-free vuln.
The fix is to never kfree(as102_dev_t) directly once usb_register_dev() has succeeded. After deregistration, defer freeing memory to .release().
In other words, let release() perform the last kfree when the final open FD is closed.
Cc: stable@vger.kernel.org Reported-by: syzbot+47321e8fd5a4c84088db@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=47321e8fd5a4c84088db Fixes: cd19f7d3e39b ("[media] as102: fix leaks at failure paths in as102_usb_probe()") Signed-off-by: Jeongjun Park aha310510@gmail.com
v2: Fix incorrect patch description style and CC stable mailing list
drivers/media/usb/as102/as102_usb_drv.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/media/usb/as102/as102_usb_drv.c b/drivers/media/usb/as102/as102_usb_drv.c index e0ef66a522e2..abde5666b2ee 100644 --- a/drivers/media/usb/as102/as102_usb_drv.c +++ b/drivers/media/usb/as102/as102_usb_drv.c @@ -404,6 +404,7 @@ static int as102_usb_probe(struct usb_interface *intf, as102_free_usb_stream_buffer(as102_dev); failed_stream: usb_deregister_dev(intf, &as102_usb_class_driver);
- return ret;
Here too I wonder if the memory is actually freed. I suspect a usb_put_intf() is needed. I'm not a USB expert, though. But you should check if you didn't replace a UAF by a memory leak.
Regards,
Hans
failed: usb_put_dev(as102_dev->bus_adap.usb_dev); usb_set_intfdata(intf, NULL); --
linux-stable-mirror@lists.linaro.org
-
Hans Verkuil -
Jeongjun Park