netdev - Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases

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: <831f64a3-1421-4d61-a2ff-3ac17378c2a0@redhat.com>
Date: Tue, 22 Apr 2025 13:34:27 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
 jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, toke@...hat.com,
 gerrard.tai@...rlabs.sg, pctammela@...atatu.com,
 Victor Nogueira <victor@...atatu.com>
Subject: Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue
 cases

On 4/17/25 6:07 PM, Jakub Kicinski wrote:
> On Wed, 16 Apr 2025 07:24:22 -0300 Victor Nogueira wrote:
>> As described in Gerrard's report [1], there are cases where netem can
>> make the qdisc enqueue callback reentrant. Some qdiscs (drr, hfsc, ets,
>> qfq) break whenever the enqueue callback has reentrant behaviour.
>> This series addresses these issues by adding extra checks that cater for
>> these reentrant corner cases. This series has passed all relevant test
>> cases in the TDC suite.
> 
> Sorry for asking this question a bit late, but reentrant enqueue seems
> error prone. Is there a clear use case for netem as a child?
> If so should we also add some sort of "capability" to avoid new qdiscs
> falling into the same trap, without giving the problem any thought?

AFAIK netem use is quite widespread, even outside testing scenarios. I
suspect preventing netem from nesting under arbitrary root could break
multiple ("unusual") users.

Cheers,

Paolo