linux-kernel - Re: [PATCH RFC v2 5/22] selinux: avoid nontransitive comparison

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Message-ID: <CAJ2a_DegsCWSB224rFVNjs7QOy0xR-k5OhoQuSvpT7w_+RD_ew@mail.gmail.com>
Date: Wed, 8 Jan 2025 16:06:49 +0100
From: Christian Göttsche <cgzones@...glemail.com>
To: Paul Moore <paul@...l-moore.com>
Cc: Christian Göttsche <cgoettsche@...tendoof.de>, 
	selinux@...r.kernel.org, Stephen Smalley <stephen.smalley.work@...il.com>, 
	Ondrej Mosnacek <omosnace@...hat.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Thiébaud Weksteen <tweek@...gle.com>, 
	Bram Bonné <brambonne@...gle.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH RFC v2 5/22] selinux: avoid nontransitive comparison

On Wed, 8 Jan 2025 at 14:17, Christian Göttsche <cgzones@...glemail.com> wrote:
>
> On Wed, 8 Jan 2025 at 04:00, Paul Moore <paul@...l-moore.com> wrote:
> >
> > On Dec 16, 2024 =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgoettsche@...tendoof.de> wrote:
> > >
> > > Avoid using nontransitive comparison to prevent unexpected sorting
> > > results due to (well-defined) overflows.
> > > See https://www.qualys.com/2024/01/30/qsort.txt for a related issue in
> > > glibc's qsort(3).
> > >
> > > Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> > > ---
> > >  security/selinux/ss/policydb.c | 18 ++++++++++--------
> > >  1 file changed, 10 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
> > > index 3ba5506a3fff..eb944582d7a6 100644
> > > --- a/security/selinux/ss/policydb.c
> > > +++ b/security/selinux/ss/policydb.c
> > > @@ -37,6 +37,8 @@
> > >  #include "mls.h"
> > >  #include "services.h"
> > >
> > > +#define spaceship_cmp(a, b) (((a) > (b)) - ((a) < (b)))
> >
> > I'll admit that it took me a while to figure out why you decided to
> > name this macro "spaceship_cmp", and then I had a little laugh when
> > I realized why it was called the "spaceship" operator :)
> >
> > Anyway, while the spaceship operator is likely familiar to people who
> > have a Perl background, the kernel is still mostly a C project so I
> > don't think we can expect a base understanding of Perl, especially
> > these days as Perl isn't as popular as in the past.  Can we rename
> > this to something else that makes more sense in the context of C?
>
> There seem to be 4 similar macros already in the kernel, 3 named
> cmp_int() and one instance named cmp_ptr().
> So I am going with cmp_int() in v3 for now, but I am open for other suggestions.

p.s.: C++ also had takeoff:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0515r3.pdf

> >
> > --
> > paul-moore.com