CVE-2021-46906: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-46906 is a vulnerability discovered in the Linux kernel's HID (Human Interface Device) USB handling component. The issue was publicly disclosed on February 25, 2024, and affects the hid_submit_ctrl function in the kernel's USB HID implementation. The vulnerability exists because the function doesn't properly account for cases where report->size can be zero, leading to potential information leakage (CVE Details).

The vulnerability occurs in the hid_submit_ctrl() function where the calculation of report length doesn't properly handle cases when report->size is zero. When a report of size 0 is processed, hid_submit_ctrl() calculates transfer_buffer_length as 16384 bytes. When this URB (USB Request Block) is passed to the USB core layer, KMSAN (Kernel Memory Sanitizer) reports an information leak of 16384 bytes. The fix involves modifying hid_report_len() to use DIV_ROUND_UP for the division to properly account for zero report size cases (Kernel Commit).

The vulnerability can lead to information leakage of up to 16384 bytes from kernel memory when exploited. This could potentially expose sensitive information from the kernel space to unauthorized users (Red Hat).

The vulnerability has been fixed in various Linux kernel versions. Ubuntu has released fixes for multiple versions: 5.4.0-81.91 for focal (20.04 LTS), 4.15.0-156.163 for bionic (18.04 LTS), and 4.4.0-258.292 for xenial (16.04 LTS). The fix involves updating the hid_report_len() function to properly handle zero-sized reports (Ubuntu).