A flaw was found in the Linux kernel's ext4 filesystem. A local user can
cause an out-of-bound access in ext4_get_group_info function, a denial of
service, and a system crash by mounting and operating on a crafted ext4
filesystem image.

Wen Xu discovered that the ext4 filesystem implementation in the Linux
kernel did not properly keep meta-data information consistent in some
situations. An attacker could use this to construct a malicious ext4 image
that, when mounted, could cause a denial of service (system crash).

 sbeattie> possible reproducer in bug report