If a zero length is passed to kmalloc() it returns 0x10, which is
not a valid address. gss_verify_mic() subsequently crashes when it
attempts to dereference that pointer.
Instead of allocating this memory on every call based on an
untrusted size value, use a piece of dynamically-allocated scratch
memory that is always available.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
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