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If busid is registered using match_busid but the device is never bound to the driver or it is never 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. Add usb_get_dev in addition to the null check to get a reference to udev to prevent udev from becoming NULL after the check. Drop the reference after using it in do_rebind(). Reported-by: syzbot+af76b01c9a0f0ab60fb0@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=af76b01c9a0f0ab60fb0 Fixes: 4bfb141bc013 ("usbip: usbip_host: fix to hold parent lock for device_attach() calls") Cc: stable@vger.kernel.org Signed-off-by: Jeffin Philip --- Changes in v2: - Addressed concerns raised by the maintainer in v1 discussion - Added usb_get_dev() to get a reference to udev preventing it from becoming null after the null check. Drop the reference after using it in do_rebind() --- drivers/usb/usbip/stub_main.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c index 79110a69d697..c911626427dc 100644 --- a/drivers/usb/usbip/stub_main.c +++ b/drivers/usb/usbip/stub_main.c @@ -256,12 +256,21 @@ 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; + } + + /* get a reference to udev to prevent it from becoming NULL */ + usb_get_dev(bid->udev); /* mark the device for deletion so probe ignores it during rescan */ bid->status = STUB_BUSID_OTHER; /* release the busid lock */ put_busid_priv(bid); ret = do_rebind((char *) buf, bid); + /* we finished using udev and don't need the reference anymore, drop it */ + usb_put_dev(bid->udev); if (ret < 0) return ret; -- 2.55.0