CVE-2026-98773USB: cdc-acm: skip URB restart in port_shutdown if disconnected

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/d97da42e9de577dc827d4e8866e6971deefe2d9c
• https://git.kernel.org/stable/c/d86775e79838d7d2e38ccf506a7d0f8e2dd4d5d0
• https://git.kernel.org/stable/c/9742905d9ed5bf23ebe4c100dec80b6bc50fb522
• https://git.kernel.org/stable/c/a0ed07b5bbb2d8fcef86810453216070691816e7
• https://git.kernel.org/stable/c/420ca35af891d33522cc08504768ccd60a4c450a
• https://git.kernel.org/stable/c/dc614d6bc991740d41d5a99ac7765c4b675dda88