Re: [PATCH RESEND v5 2/5] namei: O_BENEATH-style path resolution flags

[Aleksa Sarai]

On 2019-03-09, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, Mar 9, 2019 at 9:26 AM Christian Brauner <christian@xxxxxxxxxx> wrote:
> > Aside from that I want to point out that it is non-trivial to do this in
> > user space.
> 
> Oh, absolutely agreed. It's easy to do it in the kernel, and doing it
> anywhere else ends up having horrible races that the kernel has to
> deal with and has long solved anyway.

We've seen in the past few years, there are also plenty of CVEs from the
container runtime side of things which show that some of these races are
also exploitable. Even with some of the most convoluted O_PATH "fd
re-opening" trickery, it's incredibly difficult to both scope symlinks
inside a container and safely detect cases where you've been tricked by
a malicious actor.

> I've only seen this (2/5) patch, so I won't comment on the other ones,
> but this still makes sense to me.

I'll make sure to add you to the series Cc if/when there's a v6.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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