Messages in this thread | | | Date | Tue, 21 May 2002 15:04:22 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: AUDIT: copy_from_user is a deathtrap. |
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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
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