Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

In the Linux kernel, the following vulnerability has been resolved:

net: usb: aqc111: Do not perform PM inside suspend callback

syzbot reports "task hung in rpm_resume"

This is caused by aqc111_suspend calling the PM variant of its write_cmd routine.

The simplified call trace looks like this:

rpm_suspend() usb_suspend_both() - here udev->dev.power.runtime_status == RPM_SUSPENDING aqc111_suspend() - called for the usb device interface aqc111_write32_cmd() usb_autopm_get_interface() pm_runtime_resume_and_get() rpm_resume() - here we call rpm_resume() on our parent rpm_resume() - Here we wait for a status change that will never happen.

At this point we block another task which holds rtnl_lock and locks up the whole networking stack.

Fix this by replacing the write_cmd calls with their _nopm variants