The pmd_none_or_trans_huge_or_clear_bad function in include/asm-generic/pgtable.h in the Linux kernel before 3.13 on NUMA systems does not properly determine whether a Page Middle Directory (PMD) entry is a transparent huge-table entry, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via a crafted MADV_WILLNEED madvise system call that leverages the absence of a page-table lock.