[Linux-kernel-mentees] [PATCH] Media: Radio: Change devm_k*alloc to k*alloc

[Luke Nowakowski-Krijger]

This patch aims to fix the use-after-free read described in
https://syzkaller.appspot.com/bug?extid=a4387f5b6b799f6becbf

Changes devm_k*alloc to k*alloc which manually frees memory allocated by
raremono_device instead of leaving it to be automatically deallocated
when the USB interface calls it to be freed. The devices resources are
freed in usb_raremono_disconnect as well as freed when error conditions
occur in usb_raremono_probe.

This change is necessary due to the fact that when the USB device is
disconnected, it frees the raremono_device structure before doing the
necessary cleanup to remove references to the device, thus we get these
use-after-free errors.

I would like to thank Hans Verkuil for pointing me in the right
direction to fix this issue.

Signed-off-by: Luke Nowakowski-Krijger <lnowakow at eng.ucsd.edu>

---
  drivers/media/radio/radio-raremono.c | 18 +++++++++++++-----
  1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/media/radio/radio-raremono.c b/drivers/media/radio/radio-raremono.c
index 5e782b3c2fa9..88cff46cde28 100644
--- a/drivers/media/radio/radio-raremono.c
+++ b/drivers/media/radio/radio-raremono.c
@@ -171,6 +171,8 @@ static void usb_raremono_disconnect(struct usb_interface *intf)
         v4l2_device_disconnect(&radio->v4l2_dev);
         mutex_unlock(&radio->lock);
         v4l2_device_put(&radio->v4l2_dev);
+       kfree(radio->buffer);
+       kfree(radio);
  }

  /*
@@ -295,12 +297,15 @@ static int usb_raremono_probe(struct usb_interface *intf,
         struct raremono_device *radio;
         int retval = 0;

-       radio = devm_kzalloc(&intf->dev, sizeof(struct raremono_device), GFP_KERNEL);
-       if (radio)
-               radio->buffer = devm_kmalloc(&intf->dev, BUFFER_LENGTH, GFP_KERNEL);
-
-       if (!radio || !radio->buffer)
+       radio = kzalloc(sizeof(struct raremono_device), GFP_KERNEL);
+       if (!radio)
+               return -ENOMEM;
+
+       radio->buffer = kmalloc(BUFFER_LENGTH, GFP_KERNEL);
+       if (!radio->buffer) {
+               kfree(radio);
                 return -ENOMEM;
+       }

         radio->usbdev = interface_to_usbdev(intf);
         radio->intf = intf;
@@ -324,6 +329,9 @@ static int usb_raremono_probe(struct usb_interface *intf,
         if (retval != 3 ||
             (get_unaligned_be16(&radio->buffer[1]) & 0xfff) == 0x0242) {
                 dev_info(&intf->dev, "this is not Thanko's Raremono.\n");
+
+               kfree(radio->buffer);
+               kfree(radio);
                 return -ENODEV;
         }

-- 
2.20.1