linux-kernel - Re: [Patch v2] mm/vmscan: fix unsequenced modification and access warning

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]

Date:   Thu, 25 May 2017 21:43:43 -0700
From:   Nick Desaulniers <nick.desaulniers@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        mgorman@...hsingularity.net, vbabka@...e.cz, minchan@...nel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v2] mm/vmscan: fix unsequenced modification and access
 warning

On Tue, May 16, 2017 at 10:27:46AM +0200, Michal Hocko wrote:
> I guess it is worth reporting this to clang bugzilla. Could you take
> care of that Nick?

>From https://bugs.llvm.org//show_bug.cgi?id=33065#c5
it seems that this is indeed a sequence bug in the previous version of
this code and not a compiler bug.  You can read that response for the
properly-cited wording but my TL;DR/understanding is for the given code:

struct foo bar = {
  .a = (c = 0),
  .b = c,
};

That the compiler is allowed to reorder the initializations of bar.a and
bar.b, so what the value of c here might not be what you expect.