Re: [RFC 0/2] fix in-kernel segfault

[Jens Axboe <axboe@kernel.dk>]

On 11/24/19 1:57 AM, Pavel Begunkov wrote:
> On 24/11/2019 02:08, Jens Axboe wrote:
>> On 11/23/19 3:49 PM, Pavel Begunkov wrote:
>>> There is a bug hunging my system when run fixed-link with /dev/urandom
>>> instead of /dev/zero (see patch 1/2).
>>>
>>> As for me, the easiest way to fix is to grab mm and use userspace
>>> address for this specific case (as it's done in patches). The other
>>> way is to kmap/vmap, but the first should be short-lived and the
>>> second needs mm anyway.
>>>
>>> Ideas how to do it better way? Suggestions and corrections are welcome.
>>
>> OK, took a quick look. kmap() etc doesn't need context, but the copy
> 
> Thanks! What copy do you mean? The first and pretty short version was
> with kmap.
> e.g. while(count) { read(kmap()); ...; knumap(); }
> 
> I'll send this shortly. What I don't like here, is that it passes
> kmapped virtual address as "void __user *". Is that ok?

I think that's OK, it is a user address, after all. Stripping the other
way is usually a bigger concern :-)

-- 
Jens Axboe