Linux Kernel GFS2 CVE-2026-43262

GFS2 (Global File System 2) is a shared-disk cluster filesystem integrated into the Linux kernel, used primarily in Red Hat Enterprise Linux cluster deployments. It coordinates inode access across cluster nodes using distributed locks called glocks. The fiemap ioctl (FIEMAP) enumerates a file's physical extent mappings; gfs2_fiemap() acquires the inode glock before calling iomap_fiemap() to perform this enumeration. The defect arises when the userspace-supplied output buffer passed to fiemap is backed by a memory mapping (mmap) of the same GFS2 inode: writing fiemap results into that buffer triggers a page fault, which in turn requires the kernel to acquire the inode glock - a lock the current execution context already holds. This recursive glock acquisition produces a deadlock, freezing the kernel thread and rendering the GFS2 mount unresponsive. CWE-401 (Missing Release of Memory) is listed but is a mislabeling; the root cause is improper lock re-entrancy (closer to CWE-667: Improper Locking). The fix disables page faults during iomap_fiemap() and manually faults in the userspace buffer before proceeding, breaking the recursive lock chain. Affected CPE: cpe:2.3:a:linux:linux:*:*:*:*:*:*:*:*.