Re: AUDIT: copy_from_user is a deathtrap.

Linus Torvalds
2002-05-21T22:04:46Z

On Tue, 21 May 2002, Andrew Morton wrote:
>
> Pavel makes a reasonable point that copy_*_user may elect
> to copy the data in something other than strictly ascending
> user virtual addresses. In which case it's not possible to return
> a sane "how much was copied" number.

I don't agree that that is true.

Do you have _any_ reasonable implementation taht would do that_

> And copy_*_user is buggy at present: it doesn't correctly handle
> the case where the source and destination of the copy are overlapping
> in the same physical page. Example code below.

So we have memcpy() semantics for read()/write(), big deal.

The same way you aren't supposed to use memcpy() for overlapping areas,
you're not supposed to read/write into such areas, for all the same
reasons.

> One fix is to
> do the copy with descending addresses if src<dest or whatever.

No. That wouldn't work anyway, because the addresses are totally different
kinds.

> But then how to return the number of bytes??

The way we do now, which is the CORRECT way.

Stop this idiocy.

The current interface is quite well-defined, and has good semantics. Every
single argument against it has been totally bogus, with no redeeming
values.

Linus