linux-kernel - Re: [PATCH] net: check negative value for signed refcnt

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: <7bc31b61-8852-88a7-12bf-494c0e54574b@gmail.com>
Date:   Thu, 31 Jan 2019 07:15:53 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        alexandre.besnard@...tathome.com, davem@...emloft.net,
        ecree@...arflare.com, jiri@...lanox.com, petrm@...lanox.com,
        alexander.h.duyck@...el.com, amritha.nambiar@...el.com,
        lirongqing@...du.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: check negative value for signed refcnt



On 01/31/2019 05:49 AM, Kirill Tkhai wrote:
> 
> 2)Not related to your patch -- it looks like we have problem in existing
> code with this netdev_refcnt_read(). It does not imply a memory ordering
> or some guarantees about reading percpu values. For example, in generic
> code struct percpu_ref switches a counter into atomic mode before it checks
> for the last reference. But there is nothing in netdev_refcnt_read().

Well, if we read an old value here, after a full and expensive synchronize_net(),
then we would have lot more problems than simply having a second round in
netdev_wait_allrefs()