Input buffer over-read in AES-XTS implementation on 64 bit ARM

Issue summary: The AES-XTS cipher decryption implementation for 64 bit ARM

platform contains a bug that could cause it to read past the input buffer,

leading to a crash.

Impact summary: Applications that use the AES-XTS algorithm on the 64 bit ARM

platform can crash in rare circumstances. The AES-XTS algorithm is usually

used for disk encryption.

The AES-XTS cipher decryption implementation for 64 bit ARM platform will read

past the end of the ciphertext buffer if the ciphertext size is 4 mod 5 in 16

byte blocks, e.g. 144 bytes or 1024 bytes. If the memory after the ciphertext

buffer is unmapped, this will trigger a crash which results in a denial of

service.

If an attacker can control the size and location of the ciphertext buffer

being decrypted by an application using AES-XTS on 64 bit ARM, the

application is affected. This is fairly unlikely making this issue

a Low severity one.