tty: port: fix tty_port_tty_vhangup() race

Overview

In the Linux kernel, the following vulnerability has been resolved:

tty: port: fix tty_port_tty_vhangup() race

Drivers rely on tty_port_tty_vhangup() to synchronously hang up their ports before tearing down resources as part of deregistration (e.g. on physical disconnect).

If tty_port_tty_vhangup() races with another hangup it may however return before the port has been shut down. This is in turn can lead to use-after-free and NULL-pointer dereferences in racing ioctls (including a synchronous hangup) and in processing of racing asynchronous hangups (carrier loss).

Add the missing serialisation to tty_port_tty_vhangup() and tty_port_hangup() so that the former does not return until the port has been shut down also when there is a racing hangup.

Note that serial core does not use tty_port_hangup(), but it already holds the port mutex when clearing port->tty and shutting down the port in uart_hangup().

Affected

• Linux >= 7ca0ff9ab3218ec443a7a9ad247e4650373ed41e < 6d1a984afc3ca477dab3e51ec806671d443ad524
• Linux >= 7ca0ff9ab3218ec443a7a9ad247e4650373ed41e < 6b7be3b9b857947e9c1338d4919d4ebd3b75e907
• Linux >= 7ca0ff9ab3218ec443a7a9ad247e4650373ed41e < 017b18addbe8dcace1a569a00d40ed1ba1e03f4c
• Linux >= 7ca0ff9ab3218ec443a7a9ad247e4650373ed41e < b48820de8c1a596c5b99775524dfce73c6576c5d
• Linux 4260dc792fabfd20c8644fa9414b2ae48372365f
• Linux >= 2.6.31.2 < 2.6.32
• Linux 2.6.32

Remediation

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