CVE-2026-43327

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> USB: dummy-hcd: Fix locking/synchronization error<br /> <br /> Syzbot testing was able to provoke an addressing exception and crash<br /> in the usb_gadget_udc_reset() routine in<br /> drivers/usb/gadgets/udc/core.c, resulting from the fact that the<br /> routine was called with a second ("driver") argument of NULL. The bad<br /> caller was set_link_state() in dummy_hcd.c, and the problem arose<br /> because of a race between a USB reset and driver unbind.<br /> <br /> These sorts of races were not supposed to be possible; commit<br /> 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"),<br /> along with a few followup commits, was written specifically to prevent<br /> them. As it turns out, there are (at least) two errors remaining in<br /> the code. Another patch will address the second error; this one is<br /> concerned with the first.<br /> <br /> The error responsible for the syzbot crash occurred because the<br /> stop_activity() routine will sometimes drop and then re-acquire the<br /> dum-&gt;lock spinlock. A call to stop_activity() occurs in<br /> set_link_state() when handling an emulated USB reset, after the test<br /> of dum-&gt;ints_enabled and before the increment of dum-&gt;callback_usage.<br /> This allowed another thread (doing a driver unbind) to sneak in and<br /> grab the spinlock, and then clear dum-&gt;ints_enabled and dum-&gt;driver.<br /> Normally this other thread would have to wait for dum-&gt;callback_usage<br /> to go down to 0 before it would clear dum-&gt;driver, but in this case it<br /> didn&amp;#39;t have to wait since dum-&gt;callback_usage had not yet been<br /> incremented.<br /> <br /> The fix is to increment dum-&gt;callback_usage _before_ calling<br /> stop_activity() instead of after. Then the thread doing the unbind<br /> will not clear dum-&gt;driver until after the call to<br /> usb_gadget_udc_reset() safely returns and dum-&gt;callback_usage has been<br /> decremented again.