cifs_copy_sid(struct cifs_sid *dst, const struct cifs_sid *src)
{
	int i;

	dst->revision = src->revision;
	dst->num_subauth = min_t(u8, src->num_subauth, SID_MAX_SUB_AUTHORITIES);
	for (i = 0; i < NUM_AUTHS; ++i)
		dst->authority[i] = src->authority[i];
	for (i = 0; i < dst->num_subauth; ++i)
		dst->sub_auth[i] = src->sub_auth[i];
}

The product dereferences a pointer that it expects to be valid but is NULL.