What is the point of using the linux macro access_ok()

If __lddk_copy_from_user() simply calls copy_from_user(), then the access_ok() checks are redundant, because copy_from_user() performs these checks itself.

The access_ok() checks ensure that the userspace application isn't asking the kernel to read from or write to kernel addresses (they're an integrity/security check). Just because a pointer was supplied by userspace doesn't mean that it's definitely a userspace pointer - in many cases "kernel pointer" simply means that it's pointing within a particular region of the virtual address space.

Additionally, calling access_ok() with VERIFY_WRITE implies VERIFY_READ, so if you check the former you do not need to also check the latter.

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As of this commit in 2019, access_ok() no long has the type argument, so the VERIFY_WRITE versus VERIFY_READ point is moot.