USB: cdc-acm: skip URB restart in port_shutdown if disconnected

Summary

In the Linux kernel, the following vulnerability has been resolved: USB: cdc-acm: skip URB restart in port_shutdown if disconnected acm_port_shutdown() is called from the tty-port machinery whenever the last user closes the port. acm_disconnect() sets acm->disconnected and calls tty_port_tty_vhangup(), which eventually triggers port_shutdown(). At that point acm_disconnect() has already called acm_poison_urbs() and is about to free the control and read URBs. However, acm_port_shutdown() unconditionally calls acm_unpoison_urbs() and, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the ctrlurb and all read URBs. If the concurrent acm_disconnect() then frees those URBs and their DMA buffers while they are in-flight, the result is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback() accessing the freed DMA memory. Fix by checking acm->disconnected after draining the delayed anchor and returning early: if we are in a disconnect path the URBs must remain poisoned and must not be resubmitted. The early return is placed after the delayed-anchor drain loop because that loop only cancels write-side accounting (wb->use = false and autopm counter) and does not touch the hardware path.

Timeline

1. Oct 18, 2026, 3:48 PM UTCCVE published
2. Oct 30, 2026, 12:39 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 6.1.175 · fixed in 6.1.191; From 6.6.136 · fixed in 6.6.160; From 6.12.83 · fixed in 6.12.113; From 6.18.24 · fixed in 6.18.56; From 6.19.14 · fixed in 6.20; From 7.0.1 · fixed in 7.1

• Linux Linux

  7.1

• KernelLinux

  fixed in 6.6.160; From 6.7.0 · fixed in 6.12.113; From 6.13.0 · fixed in 6.18.56; From 6.19.0 · fixed in 7.2.10

References 6