The ext4_isize function in fs/ext4/ext4.h in the Linux kernel 2.6.27 before 2.6.27.19 and 2.6.28 before 2.6.28.7 uses the i_size_high structure member during operations on arbitrary types of files, which allows local users to cause a denial of service (CPU consumption and error-message flood) by attempting to mount a crafted ext4 filesystem.