linux-kernel - Re: [PATCH] libbpf: Fix integer overflow issue

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Message-ID: <32f7b86c2426819f75388dbb1deb27c846a99b03.camel@gmail.com>
Date: Tue, 08 Oct 2024 10:34:28 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: I Hsin Cheng <richard120310@...il.com>, martin.lau@...ux.dev, 
	ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: Fix integer overflow issue

On Tue, 2024-10-08 at 10:21 -0700, Andrii Nakryiko wrote:
> On Tue, Oct 8, 2024 at 2:49 AM Eduard Zingerman <eddyz87@...il.com> wrote:
> > 
> > On Mon, 2024-10-07 at 20:42 -0700, Andrii Nakryiko wrote:
> > 
> > [...]
> > 
> > > Not sure what Eduard is suggesting here, tbh. But I think if this
> > > actually can happen that we have a non-loaded BPF program in one of
> > > those struct_ops slots, then let's add a test demonstrating that.
> > 
> > Given the call chain listed in a previous email I think that such
> > situation is not possible (modulo obj->gen_loader, which I know
> > nothing about).
> > 
> > Thus I suggest to add a pr_warn() and return -EINVAL or something like
> > that here.
> > 
> 
> That's what confused me :) If it's impossible, there is no need to
> handle it, we know the FD has to be there. So I'd just not change
> anything.

Granted I have a memory of a fruit fly, but it took me like half an
hour to figure out if it is possible or not, and I wrote a part of
that code. At the very least a comment is needed.
Also, adding an explicit cast should silence the tool warning.

> 
> > > Worst case of what can happen right now is the kernel rejecting
> > > struct_ops loading due to -22 as a program FD.
> > > 
> > > pw-bot: cr
> > 
> > [...]
> >