linux-kernel - Re: [RFC PATCH] piped/ptraced coredump (was: Dump smaller VMAs first in ELF cores)

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Message-ID: <CAHk-=whg0d5rxiEcPFApm+4FC2xq12sjynDkGHyTFNLr=tPmiw@mail.gmail.com>
Date: Sun, 4 Aug 2024 10:47:23 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Brian Mak <makb@...iper.net>, "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] piped/ptraced coredump (was: Dump smaller VMAs first
 in ELF cores)

On Sun, 4 Aug 2024 at 08:23, Oleg Nesterov <oleg@...hat.com> wrote:
>
> What do you think?

Eww. I really don't like giving the dumper ptrace rights.

I think the real limitations of the "dump to pipe" is that it's just
being very stupid. Which is fine in the sense that core dumps aren't
likely to be a huge priority. But if or when they _are_ a priority,
it's not a great model.

So I prefer the original patch because it's also small, but it's
conceptually much smaller.

That said, even that simplified v2 looks a bit excessive to me.

Does it really help so much to create a new array of core_vma_metadata
pointers - could we not just sort those things in place?

Also, honestly, if the issue is core dump truncation, at some point we
should just support truncating individual mappings rather than the
whole core file anyway. No?

Depending on what the major issue is, we might also tweak the
heuristics for which vmas get written out.

For example, I wouldn't be surprised if there's a fair number of "this
read-only private file mapping gets written out because it has been
written to" due to runtime linking. And I kind of suspect that in many
cases that's not all that interesting.

Anyway, I assume that Brian had some specific problem case that
triggered this all, and I'd like to know a bit more.

           Linus