[PATCH] hidraw: Fix crash on HIDIOCGFEATURE with a destroyed device

[Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>]

Doing `ioctl(HIDIOCGFEATURE)` in a tight loop on a hidraw device
and then disconnecting the device, or unloading the driver, can
cause a NULL pointer dereference.

When a hidraw device is destroyed it sets 0 to `dev->exist`.
Most functions check 'dev->exist' before doing its work, but
`hidraw_get_report()` was missing that check.

Signed-off-by: Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>
---
 drivers/hid/hidraw.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 5fbe0f81ab2e..01b5a9f01814 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -192,6 +192,11 @@ static ssize_t hidraw_get_report(struct file *file, char __user *buffer, size_t
 	int ret = 0, len;
 	unsigned char report_number;
 
+	if (!hidraw_table[minor] || !hidraw_table[minor]->exist) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	dev = hidraw_table[minor]->hid;
 
 	if (!dev->ll_driver->raw_request) {
-- 
2.16.3