Re: [PATCH 5/6] lib: Fix function documentation for strncpy_from_user

[Kees Cook]

On Mon, Feb 18, 2019 at 4:52 PM Jann Horn <jannh@xxxxxxxxxx> wrote:
> AFAICS the byte_at_a_time loop exits when max==0 is reached, and then
> if `res >= count` (in other words, if we've copied as many bytes as
> requested, haven't encountered a null byte so far, and haven't reached
> the end of the address space), we return `res`, which is the same as
> `count`. Are you sure?

Oh, whew, there is only 1 arch-specific implementation of this. I
thought you meant there was multiple implementations.

So, generally speaking, I'd love to split all strncpy* uses into
strscpy_zero() (when expecting to do str->str copies), and some new
function, named like mempadstr() or str2mem() that copies a str to a
__nonstring char array, with trailing padding, if there is space. Then
there is no more mixing the two cases and botching things.

-- 
Kees Cook