CVE-2025-39788: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-39788 is a vulnerability discovered in the Linux kernel, specifically affecting the SCSI UFS Exynos driver. The vulnerability was disclosed on September 11, 2025, and involves incorrect programming of HCIUTRLNEXUS_TYPE on Google gs101 devices (NVD, Red Hat).

The vulnerability occurs when the number of UTP transfer request slots (nutrs) is 32, causing the driver to program the UTRLNEXUSTYPE incorrectly as 0. This happens because the left-hand side of the shift operation is 1, which is of type int (31 bits wide), and shifting by more than that width results in undefined behavior. The vulnerability has been assigned a CVSS v3.1 score of 5.5 with vector AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (Red Hat).

The vulnerability affects the Linux kernel's SCSI subsystem, specifically the UFS Exynos driver. The impact is primarily related to system stability and potential undefined behavior in the affected driver's operation (NVD).

The vulnerability has been fixed by switching to the BIT() macro, which applies correct type casting as required. This ensures the correct value (0xffffffff on gs101) is written to UTRLNEXUSTYPE. The same fix has been applied to the nutmrs / UTMRLNEXUSTYPE write for consistency (Debian).