CVE-2023-54194

Description

CVE-2023-54194 addresses a memory allocation failure in the Linux kernel's exfat file system driver when mounting removable media such as USB disks. The bug occurred in the load_alloc_bitmap function, which used kmalloc_array to allocate memory for the allocation bitmap. In long-running systems, physical memory fragmentation can prevent kmalloc_array from allocating contiguous pages, leading to a kernel warning and mount failure [1].

Attack

Vector and Requirements

To trigger the vulnerability, an attacker needs physical access to the system to insert a removable device formatted with exfat, or the ability to cause such a device to be connected. No special privileges are required beyond the ability to mount a filesystem. The condition manifests when the system has been running for an extended period and system memory is fragmented, causing a high-order allocation to fail [1].

Impact

When triggered, the kernel logs a "page allocation failure" warning and the exfat filesystem fails to mount, making the device inaccessible. This constitutes a denial of service (DoS) for the removable storage functionality. The vulnerability does not allow privilege escalation or arbitrary code execution; it only prevents legitimate use of exfat-formatted media [1].

Mitigation

The fix changes the allocation from kmalloc_array to kvmalloc_array, which can fall back to vmalloc if contiguous physical memory is unavailable, and uses kvfree for deallocation [1]. The patch has been applied to the upstream Linux kernel and should be backported to stable kernels as needed. Users should update their kernel to include the fix or apply the patch from the stable commit [1]. No workaround is available other than avoiding exfat on fragmented systems or ensuring sufficient contiguous memory.