serial: 8250_bcm7271: fix use-after-free in brcmuart_remove()

Overview

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

serial: 8250_bcm7271: fix use-after-free in brcmuart_remove()

brcmuart_handle_irq() starts priv->hrt to work around a receive-timeout quirk of the 8250 core when hardware flow control is enabled; the timer callback brcmuart_hrtimer_func() dereferences priv.

brcmuart_remove() cancels the hrtimer before it unregisters the port, so a receive-timeout interrupt that arrives in between re-arms the timer. After devm frees priv, the callback runs on freed memory.

Unregister the port before cancelling the hrtimer. serial8250_unregister_port() shuts the port down and frees its IRQ, so brcmuart_handle_irq() can no longer restart the timer, and the final hrtimer_cancel() drains any timer that was armed before or during the unregister.

This issue was found by an in-house static analysis tool.

Affected

• Linux >= 41a469482de257ea8db43cf74b6311bd055de030 < f5ce06e648d775cc1ccf66f4f594bb8b559a7d8e
• Linux >= 41a469482de257ea8db43cf74b6311bd055de030 < e32440fa536af96bdbc61d933a7c3a920b965edc
• Linux >= 41a469482de257ea8db43cf74b6311bd055de030 < 0794ba5332754866b2f1c0cca668775be3ffcf0a
• Linux >= 41a469482de257ea8db43cf74b6311bd055de030 < 189b9dc8c96ec9486482f27c1372b04a7152175e
• Linux 5.13

Remediation

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