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).
CVSS Details
- CVSS 3.1 Base Score: 5.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade kernel-develUpgrade kernel-tools-debuginfoUpgrade kernel-headersUpgrade python-perf-debuginfoUpgrade kernelUpgrade kernel-debuginfoUpgrade perf-debuginfoUpgrade perfUpgrade kernel-tools-develUpgrade kernel-livepatch-5.15.57-29.131Upgrade kernel-debuginfo-common-x86_64Upgrade python-perfUpgrade kernel-toolsUpgrade bpftool-debuginfoUpgrade bpftoolUpgrade kernel-livepatch-5.10.135-122.509Upgrade kernel-debuginfo-common-aarch64 | May 22, 2025 | Feb 26, 2025 |
| Debian | — | Upgrade linux | Feb 27, 2025 | Feb 27, 2025 |
| Huawei Euleros 2_0_sp13 | — | Upgrade kernel-abi-stablelistsUpgrade kernel-toolsUpgrade python3-perfUpgrade kernelUpgrade bpftoolUpgrade kernel-tools-libs | Jul 1, 2025 | Feb 26, 2025 |
| Redhat_linux | — | No solution exists | Jul 9, 2025 | Feb 26, 2025 |
| Ubuntu | — | Upgrade linux-realtimeUpgrade linux-oracleUpgrade linux-intel-iotg-5.15Upgrade linux-gcp-5.15Upgrade linux-gkeUpgrade linux-kvmUpgrade linux-oracle-5.15Upgrade linux-lowlatencyUpgrade linux-awsUpgrade linux-lowlatency-hwe-5.15Upgrade linux-raspiUpgrade linux-aws-5.15Upgrade linux-azureUpgrade linux-hwe-5.15Upgrade linux-ibmUpgrade linux-intel-iotgUpgrade linux-riscv-5.15Upgrade linuxUpgrade linux-gkeopUpgrade linux-azure-5.15Upgrade linux-gcpUpgrade linux-nvidia | Mar 19, 2025 | Feb 26, 2025 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | May 27, 2026 | Feb 26, 2025 |
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