CVE-2022-49613

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

serial: 8250: Fix PM usage_count for console handover

When console is enabled, univ8250consolesetup() calls serial8250consolesetup() before .dev is set to uartport. Therefore, it will not call pmruntimegetsync(). Later, when the actual driver is going to take over univ8250consoleexit() is called. As .dev is already set, serial8250consoleexit() makes pmruntimeputsync() call with usage count being zero triggering PM usage count warning (extra debug for univ8250consolesetup(), univ8250consoleexit(), and serial8250register_ports()):

[ 0.068987] univ8250consolesetup ttyS0 nodev [ 0.499670] printk: console [ttyS0] enabled [ 0.717955] printk: console [ttyS0] printing thread started [ 1.960163] serial8250registerports assigned dev for ttyS0 [ 1.976830] printk: console [ttyS0] disabled [ 1.976888] printk: console [ttyS0] printing thread stopped [ 1.977073] univ8250consoleexit ttyS0 usage:0 [ 1.977075] serial8250 serial8250: Runtime PM usage count underflow! [ 1.977429] dw-apb-uart.6: ttyS0 at MMIO 0x4010006000 (irq = 33, basebaud = 115200) is a 16550A [ 1.977812] univ8250console_setup ttyS0 usage:2 [ 1.978167] printk: console [ttyS0] printing thread started [ 1.978203] printk: console [ttyS0] enabled

To fix the issue, call pmruntimegetsync() in serial8250registerports() as soon as .dev is set for an uartport 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).