CVE-2026-43327
Published: May 21, 2026Last modified: May 21, 2026
Description
In the Linux kernel, the following vulnerability has been resolved: USB: dummy-hcd: Fix locking/synchronization error Syzbot testing was able to provoke an addressing exception and crash in the usb_gadget_udc_reset() routine in drivers/usb/gadgets/udc/core.c, resulting from the fact that the routine was called with a second ("driver") argument of NULL. The bad caller was set_link_state() in dummy_hcd.c, and the problem arose because of a race between a USB reset and driver unbind. These sorts of races were not supposed to be possible; commit 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"), along with a few followup commits, was written specifically to prevent them. As it turns out, there are (at least) two errors remaining in the code. Another patch will address the second error; this one is concerned with the first. The error responsible for the syzbot crash occurred because the stop_activity() routine will sometimes drop and then re-acquire the dum->lock spinlock. A call to stop_activity() occurs in set_link_state() when handling an emulated USB reset, after the test of dum->ints_enabled and before the increment of dum->callback_usage. This allowed another thread (doing a driver unbind) to sneak in and grab the spinlock, and then clear dum->ints_enabled and dum->driver. Normally this other thread would have to wait for dum->callback_usage to go down to 0 before it would clear dum->driver, but in this case it didn't have to wait since dum->callback_usage had not yet been incremented. The fix is to increment dum->callback_usage _before_ calling stop_activity() instead of after. Then the thread doing the unbind will not clear dum->driver until after the call to usb_gadget_udc_reset() safely returns and dum->callback_usage has been decremented again.
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score | 5.5 |
| Attack Vector | LOCAL |
| Attack complexity | LOW |
| Privileges required | LOW |
| User interaction | NONE |
| Scope | UNCHANGED |
| Confidentiality | NONE |
| Integrity impact | NONE |
| Availability impact | HIGH |
| Vector | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
Status
| Product | Release | Package | Status |
|---|---|---|---|
| Alpaquita Linux | 23 LTS | linux-lts | Fixed (6.1.168-r0) |
| 25 LTS | linux-lts | Fixed (6.12.81-r0) | |
| Stream | linux-lts | Fixed (6.12.85-r0) |
References
- https://git.kernel.org/stable/c/218886b2ef2dea7627d3700ab0abaf4bf9d1161f
- https://git.kernel.org/stable/c/616a63ff495df12863692ab3f9f7b84e3fa7a66d
- https://git.kernel.org/stable/c/6350c7dd33ab481ef41c931a238361490c32d15c
- https://git.kernel.org/stable/c/69ab97a693251d6a6093e630060a3c744fd58524
- https://git.kernel.org/stable/c/791966f85b439b261bf19865cf1c07c065ffb4b4
- https://git.kernel.org/stable/c/805b1833d6ed6da5086e610578a28e71bb54fbbb
- https://git.kernel.org/stable/c/cc97fb5969177cccce2e23b31298df220fc7570d
- https://git.kernel.org/stable/c/efbd9441f1e769a7aae1813d497cec09cbdff031