Re: [edk2-devel] [PATCH 0/3] MdePkg/BaseLib: Base64Decode: Make it follow its specification

["Laszlo Ersek" <lersek@redhat.com>]

On 07/01/19 13:02, Laszlo Ersek wrote:
> On 06/28/19 05:57, Gao, Zhichao wrote:

> (2a) SourceLength has nothing to do with Destination. The comment should
> be updated -- making sure that (Source + SourceLength) do not overflow
> MAX_ADDRESS is worthwhile, but the comment is misleading.

Let me re-state that.

Usually, when you expect the caller to provide an array of bytes,
identified by base address and size, the burden to provide an *actual
array* is on the caller. If the caller does not conform to the function
specification, the behavior is undefined, and it's on the caller.
Therefore, checking MAX_ADDRESS overflows is *generally* dubious, in my
opinion, because a valid array can never overflow MAX_ADDRESS.

If we want to be paranoid about this, I guess we can keep implement
MAX_ADDRESS checks, but then we should both document and implement them
correctly.

Second, it is usually good to specify whether overlap between input and
output is permitted. If we want to be paranoid, we can check that
explicitly again. I don't necessarily suggest that we implement an
overlap check, but we should likely specify in the leading comment that
overlap is not permitted. (This is similar to the "restrict" keyword
from C99.)

Thanks
Laszlo