linux-kernel - Re: [PATCH net 1/4] net-sysfs: check device is present when showing carrier

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0042d3c7d695ed7b253ccbc7786888dc3b400867.camel@sipsolutions.net>
Date: Wed, 24 Jul 2024 11:41:56 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Jamie Bainbridge <jamie.bainbridge@...il.com>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>
Cc: Jiri Pirko <jiri@...nulli.us>, "linux-kernel@...r.kernel.org"
	 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net 1/4] net-sysfs: check device is present when showing
 carrier

On Wed, 2024-07-24 at 11:35 +0200, Johannes Berg wrote:
> On Wed, 2024-07-24 at 01:46 +0000, Jamie Bainbridge wrote:
> > A sysfs reader can race with a device reset or removal.
> 
> Kind of, yes, but please check what the race actually is.
> 
> > This was fixed for speed_show with commit 4224cfd7fb65 ("net-sysfs: add
> > check for netdevice being present to speed_show") so add the same check
> > to carrier_show.
> 
> You didn't say why it's needed here, so ... why is it?
> 
> FWIW, I don't think it actually _is_ needed, since the netdev struct
> itself is still around, linkwatch_sync_dev() will not do anything that's
> not still needed anyway (the removal from list must clearly either still
> happen or nothing happens in the function). This will not call into the
> driver (which would be the problematic part).
> 
> So while I don't think this is _wrong_ per se, I also don't think it's
> necessary, nor are you demonstrating that it is.
> 
> And for userspace it should be pretty much immaterial whether it gets a
> real value or -EINVAL in the race, or -ENOENT because the file
> disappeared anyway?
> 

All of which, btw, is also true for patches 3 and 4 in this set.

For patch 2 it seems applicable.

I do wonder if ethtool itself, at least ethtool netlink, doesn't have a
similar problem though, since it just uses netdev_get_by_name() /
netdev_get_by_index()?

johannes