[PATCH] usbip: usbip_host: Fix null pointer dereference in rebind_store

[Jeffin Philip]

rebind_store calls do_rebind which dereferences udev without
checking if it is NULL. If busid is registered using match_busid
but the device is not present in the first place, it triggers a
null pointer dereference when we attempt to rebind the device.
Fix this by checking explicitly for udev first and returning
-ENODEV if udev is NULL.

Reported-by: syzbot+af76b01c9a0f0ab60fb0@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=af76b01c9a0f0ab60fb0
Fixes: 4bfb141bc013 ("usbip: usbip_host: fix to hold parent lock for device_attach() calls")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jeffin Philip <jeffinphilip14@xxxxxxxxx>
---
 drivers/usb/usbip/stub_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c
index 79110a69d697..dfaedecedb81 100644
--- a/drivers/usb/usbip/stub_main.c
+++ b/drivers/usb/usbip/stub_main.c
@@ -256,6 +256,11 @@ static ssize_t rebind_store(struct device_driver *dev, const char *buf,
 	if (!bid)
 		return -ENODEV;
 
+	if (!bid->udev) {
+		put_busid_priv(bid);
+		return -ENODEV;
+	}
+
 	/* mark the device for deletion so probe ignores it during rescan */
 	bid->status = STUB_BUSID_OTHER;
 	/* release the busid lock */
-- 
2.55.0