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

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Message-ID: <01df64ed8f6eb9e6f2780b5b0aa3be5c@paul-moore.com>
Date: Tue, 07 Jan 2025 21:59:59 -0500
From: Paul Moore <paul@...l-moore.com>
To: Christian Göttsche <cgoettsche@...tendoof.de>, selinux@...r.kernel.org
Cc: Christian Göttsche <cgzones@...glemail.com>, 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 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?

--
paul-moore.com