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

Overview

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

• Linux >= 603d5a7110832e10165d21f9a1486399457177de < 9742905d9ed5bf23ebe4c100dec80b6bc50fb522
• Linux >= 5d29d7ff8679e5a525f22da467ba33c042e8029b < a0ed07b5bbb2d8fcef86810453216070691816e7
• Linux >= f58752ebcb35e156c85cd1a82d6579c7af3b9023 < 420ca35af891d33522cc08504768ccd60a4c450a
• Linux >= f58752ebcb35e156c85cd1a82d6579c7af3b9023 < dc614d6bc991740d41d5a99ac7765c4b675dda88
• Linux d826061aa64cb28089bf4c73e301dd7928662b84
• Linux 8fb82e3555a7d56a05d8ef0edee9859f889c0860
• Linux 283f8162cc3c82086537cbc7dc01870dbeb07a91
• Linux f77f10bc76c2da86b4248269472f6d971e37828b
• Linux >= 6.12.83 < 6.12.113
• Linux >= 6.18.24 < 6.18.56
• Linux >= 6.1.175 < 6.2
• Linux >= 6.6.136 < 6.7
• Linux >= 6.19.14 < 6.20
• Linux >= 7.0.1 < 7.1
• Linux 7.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.