netdev - Re: [Cake] [PATCH] sch_cake: avoid possible divide by zero in cake

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: <0750BA89-01A1-4126-9BEF-2C6AC607A5BD@gmail.com>
Date:   Thu, 2 Jan 2020 23:58:02 +0200
From:   Jonathan Morton <chromatix99@...il.com>
To:     Wen Yang <wenyang@...ux.alibaba.com>
Cc:     Toke Høiland-Jørgensen <toke@...e.dk>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        cake@...ts.bufferbloat.net,
        Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [Cake] [PATCH] sch_cake: avoid possible divide by zero in
 cake_enqueue()

> On 2 Jan, 2020, at 11:21 am, Wen Yang <wenyang@...ux.alibaba.com> wrote:
> 
> The variables 'window_interval' is u64 and do_div()
> truncates it to 32 bits, which means it can test
> non-zero and be truncated to zero for division.
> The unit of window_interval is nanoseconds,
> so its lower 32-bit is relatively easy to exceed.
> Fix this issue by using div64_u64() instead.

That might actually explain a few things.  I approve.

Honestly the *correct* fix is for the compiler to implement division in a way that doesn't require substituting it with function calls.  As this shows, it's error-prone to do this manually.

 - Jonathan Morton