Linux Kernel CVE-2026-43163

The vulnerability resides in the Linux kernel's multiple-device (md) driver, specifically its bitmap subsystem (md_mod kernel module). The md subsystem implements software RAID, and the bitmap component tracks dirty regions for rebuild optimization. The race condition (CWE-362) exists between two concurrent kernel threads: bitmap_daemon_work(), which periodically flushes bitmap pages by iterating over bitmap->storage.filemap, and __bitmap_resize(), which reallocates that same storage structure during an array resize operation. The resize path calls md_bitmap_file_unmap() to free the existing filemap pages, but because bitmap_daemon_work() accesses filemap without holding mddev->bitmap_info.mutex, a concurrent daemon iteration can dereference a freed page pointer. The quiesce() call in the resize path does not halt the md thread, leaving the window open. The resulting General Protection Fault - a hardware fault triggered by a memory access violation - manifests at write_page+0x22b/0x3c0. The CPE cpe:2.3:a:linux:linux:*:*:*:*:*:*:*:* confirms the scope is the upstream Linux kernel across all architectures. The fix serializes bitmap updates by acquiring mddev->bitmap_info.mutex before the daemon iterates filemap.