linux-kernel - Re: [PATCH] seccomp: fix refcounter leak if fork/clone is terminated

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Date:   Mon, 5 Sep 2022 15:53:54 -0700
From:   Oleksandr Tymoshenko <ovt@...gle.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] seccomp: fix refcounter leak if fork/clone is terminated

Hi Christian,

The patch in the seccomp tree, adapted to 5.10 branch, fixed the
memory leak in my reproducer.
Thanks for working on this, I should have checked the seccomp tree first :)
Please disregard the patch in my submission.

Thank you

On Mon, Sep 5, 2022 at 1:39 AM Christian Brauner <brauner@...nel.org> wrote:
>
> On Fri, Sep 02, 2022 at 03:41:35AM +0000, Oleksandr Tymoshenko wrote:
> > release_task, where the seccomp's filter refcounter is released, is not
> > called for the case when the fork/clone is terminated midway by a
> > signal. This leaves an extra reference that prevents filter from being
> > destroyed even after all processes using it exit leading to a BPF JIT
> > memory leak. Dereference the refcounter in the failure path of the
> > copy_process function.
> >
> > Fixes: 3a15fb6ed92c ("seccomp: release filter after task is fully dead")
> > Cc: Christian Brauner <brauner@...nel.org>
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Oleksandr Tymoshenko <ovt@...gle.com>
> > ---
>
> Hey Oleksandr,
>
> Thanks for the patch! I'm really puzzled as to why we never noticed this
> and I'm trying to re-architect how this happend. But in any case,
> there's a patch in the seccomp tree that fixes this:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?id=6d17452707ca
>
> which is slighly different from your approach in that it moves
> copy_seccomp() after the point of no return. Let us know if you see any
> issues with this!
>
> Christian