Re: [RFC] situation with csum_and_copy_... API

[David Miller]

From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 19 Nov 2014 12:40:53 -0800

> On Wed, Nov 19, 2014 at 12:31 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
>>
>> But that is just my opinion, and yes I do acknowledge that we've had
>> serious holes in this area in the past.
> 
> The serious holes have generally been exactly in the "upper layers
> already check" camp, and then it turns out that some odd ioctl or
> other thing ends up doing something odd and interesting.
> 
> If Al has actual performance profiles showing that the access_ok() is
> a real problem, then fine. As a low-level optimization, I agree with
> it. But not as a "let's just drop them, and make the security rules be
> non-local and subtle, and require people to know the details of the
> whole call-chain".
> 
> Seeing a "__get_user()" and just being able to glance up in the same
> function and seeing the "access_ok()" is just a good safety net. And
> means that people don't have to waste time thinking about or looking
> for where the hell the security net really is.

Fair enough.
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