kernel: Mishandled freeing of instances in pcrypt.c can allow a local user to cause a denial of service

crypto/pcrypt.c in the Linux kernel, before 4.14.13, mishandles freeing instances, allowing a local user able to access the AFALG-based AEAD interface CONFIGCRYPTOUSERAPIAEAD and pcrypt CONFIGCRYPTOPCRYPT to cause a denial of service kfree of an incorrect pointer or possibly have unspecified othe...