CVE-2022-49613 Information

Description

In the Linux kernel the following vulnerability has been resolved:

serial: 8250: Fix PM usage_count for console handover

When console is enabled univ8250_console_setup() calls serial8250_console_setup() before .dev is set to uart_port. Therefore it will not call pm_runtime_get_sync(). Later when the actual driver is going to take over univ8250_console_exit() is called. As .dev is already set serial8250_console_exit() makes pm_runtime_put_sync() call with usage count being zero triggering PM usage count warning (extra debug for univ8250_console_setup() univ8250_console_exit() and serial8250_register_ports()):

[ 0.068987] univ8250_console_setup ttyS0 nodev [ 0.499670] printk: console [ttyS0] enabled [ 0.717955] printk: console [ttyS0] printing thread started [ 1.960163] serial8250_register_ports assigned dev for ttyS0 [ 1.976830] printk: console [ttyS0] disabled [ 1.976888] printk: console [ttyS0] printing thread stopped [ 1.977073] univ8250_console_exit ttyS0 usage:0 [ 1.977075] serial8250 serial8250: Runtime PM usage count underflow! [ 1.977429] dw-apb-uart.6: ttyS0 at MMIO 0x4010006000 (irq = 33 base_baud = 115200) is a 16550A [ 1.977812] univ8250_console_setup ttyS0 usage:2 [ 1.978167] printk: console [ttyS0] printing thread started [ 1.978203] printk: console [ttyS0] enabled

To fix the issue call pm_runtime_get_sync() in serial8250_register_ports() as soon as .dev is set for an uart_port if it has console enabled.

This problem became apparent only recently because 82586a721595 (\PM: runtime: Avoid device usage count underflows) added the warning printout. I confirmed this problem also occurs with v5.18 (w/o the warning printout obviously).

Reference

https://git.kernel.org/stable/c/190ce5cdc55d1b66ea582ac2be6fd5a72e3cc486 https://git.kernel.org/stable/c/5df66302f03f87ae8953785a882d78e911f00c55 https://git.kernel.org/stable/c/d9cb6fabc90102f9e61fe35bd0160db88f4f53b4 https://git.kernel.org/stable/c/f9b11229b79c0fb2100b5bb4628a101b1d37fbf6