Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer

[Michal Hocko]

On Wed 17-03-21 14:34:27, Greg KH wrote:
> On Wed, Mar 17, 2021 at 01:08:21PM +0100, Michal Hocko wrote:
> > Btw. I still have problems with the approach. seq_file is intended to
> > provide safe way to dump values to the userspace. Sacrificing
> > performance just because of some abuser seems like a wrong way to go as
> > Al pointed out earlier. Can we simply stop the abuse and disallow to
> > manipulate the buffer directly? I do realize this might be more tricky
> > for reasons mentioned in other emails but this is definitely worth
> > doing.
> 
> We have to provide a buffer to "write into" somehow, so what is the best
> way to stop "abuse" like this?

What is wrong about using seq_* interface directly?

> Right now, we do have helper functions, sysfs_emit(), that know to stop
> the overflow of the buffer size, but porting the whole kernel to them is
> going to take a bunch of churn, for almost no real benefit except a
> potential random driver that might be doing bad things here that we have
> not noticed yet.

I am not familiar with sysfs, I just got lost in all the indirection but
replacing buffer by the seq_file and operate on that should be possible,
no?

-- 
Michal Hocko
SUSE Labs