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SubjectRe: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, bisected, reproducable)
Linus Torvalds wrote:
> On Tue, 17 Jun 2008, Andi Kleen wrote:
>> If that fixes anything:
>> - The caller is broken because it shouldn't pass a faulting source to copy_to_user()
>> - And you broken copy_from_user error reporting which shares the same code
> Andi, I'm sorry I cc'd you. You are the author of that crap, but the bug
> seems to be that you never even understood what copy_from_user() is
> supposed to do.
> The whole *and*only* reason for copy_to/from_user() existing AT ALL is
> exactly the fact that the source or destination access can fault.

yes, but only one of them (destination for copy_to_user and source for

Or are you're describing copy_in_user()?

> I don't really see why you continually start arguing about things that are
> OBVIOUSLY BUGGY, as if they weren't buggy. Once somebody has debugged a
> buggy routine, you shouldn't argue against it.
> So here's a hint: next time I claim some code of yours is buggy, either
> just acknowledge the bug, or stay silent. You'll look smarter that way.

Ok if I'm really wrong on this (but frankly I don't see the mistake, sorry)
for my person edification: what's a legitimate case for copy_to_user()
where the source can fault?


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