Linux Kernel exFAT File System Memory Allocation Vulnerability

A memory allocation vulnerability has been identified in the Linux kernel's exFAT file system implementation, specifically in versions through 4.19. The issue arises from the use of 'kmalloc_array' for memory allocation, which can lead to failures due to system memory fragmentation. This problem becomes apparent when a USB disk using the exFAT file system is inserted, as the device may not be recognized. The vulnerability stems from the fact that long-running systems cannot ensure the continuity of physical memory, causing allocation failures. The issue can be exploited by inserting a pluggable device using the exFAT file system into the system.

Impact

The vulnerability can cause page allocation failures, leading to memory allocation errors when the exFAT file system is mounted. This can result in USB devices not being recognized by the system.

Reproduction

To reproduce this vulnerability, insert a USB disk formatted with the exFAT file system into a system running a vulnerable version of the Linux kernel. The device may not be recognized due to a memory allocation failure caused by fragmentation in the system's physical memory. This issue can be observed by monitoring the system's response to the inserted device, which should be recognized under normal circumstances.

Remediation

The vulnerability has been addressed in the Linux kernel by changing the memory allocation method for the exFAT file system from 'kmalloc_array' to 'kvmalloc_array', which is more suitable for the fragmented memory conditions. Users should upgrade to the latest version of the Linux kernel where this change has been implemented.