CVE-2023-54021

A flaw was found in the Linux kernel's ext4 filesystem block allocator. In ext4_mb_normalize_request(), the goal start was being set incorrectly (ac_f_ex instead of ac_g_ex), and boundary validation was missing. Without proper range checking, an underflow in ar->pright - size could pass an invalid value to ext4_get_group_no_and_offset(), triggering a BUG_ON assertion and crashing the kernel.

This flaw affects ext4 filesystems during block allocation operations. The incorrect variable assignment and missing bounds check can cause a kernel crash when specific allocation patterns trigger the underflow condition. The issue manifests during normal filesystem operations like file creation or extension, making it potentially triggerable by regular users writing to ext4 filesystems.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.