CVE-2021-47055: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47055 is a security vulnerability in the Linux kernel related to Memory Technology Device (MTD) subsystem permissions. The vulnerability affects the handling of locking and badblock ioctls (MEMLOCK, MEMUNLOCK, and OTPLOCK) which modify protection bits and the bad block table. This issue was discovered in various Linux kernel versions from 4.4.233 through 5.12.4 (NVD).

The vulnerability stems from improper permission checking in the MTD subsystem. The MEMLOCK, MEMUNLOCK, and OTPLOCK operations modify protection bits, while MEMSETBADBLOCK modifies the bad block table, but these operations were not properly requiring write permissions. This is particularly critical for hardware implementations where MEMLOCK might be write-once, such as in SPI-NOR flashes with their WP# tied to GND, and OTPLOCK is always write-once. The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability could allow an attacker with local access and limited privileges to modify protection bits and bad block tables without proper authorization. This could potentially lead to permanent changes in flash memory devices, especially in cases where operations like MEMLOCK are write-once or where OTPLOCK (One-Time Programmable) operations are involved (Red Hat).

The vulnerability requires local access with low privileges to exploit. The attack complexity is low, and no user interaction is required. However, the impact is primarily limited to availability, with no direct impact on confidentiality or integrity (NVD).

The vulnerability has been fixed by requiring write permissions for locking and badblock ioctls. The fix involves moving MEMLOCK, MEMUNLOCK, MEMSETBADBLOCK, and OTPLOCK operations to the 'dangerous' commands category, which requires proper write permissions (FMODE_WRITE) to execute. Multiple patches have been released for different kernel versions to address this issue (Kernel Patch).