Re: [PATCH v2 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access_begin()

[Linus Torvalds]

On Wed, Jan 22, 2020 at 12:00 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> A bit more re-organization also allows us to do the unsafe_put_user()
> unconditionally.

I meant the "user_access_begin()", of course.

Code was right, explanation was wrong.

That said, with this model, we _could_ make the

        unsafe_put_user(offset, &prev->d_off, efault_end);

be unconditional too, since now 'prev' will actually be a valid
pointer - it will match 'dirent' if there was no prev.

But since we want to test whether we had a previous entry anyway (for
the signal handling latency issue), making the write to the previous
d_reclen unconditional (and then overwriting it the next iteration)
doesn't actually buy us anything.

It was the user_access_begin() I'd rather have unconditional, since
otherwise it gets duplicated in two (very slightly) different versions
and we have unnecessary code bloat.

           Linus