linux-kernel - Re: [PATCH] selinux: remove duplicated initialization of 'i' for clean-up

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Message-ID: <CADLLry6kOGBEjfGYjS=4qCU_V=0deJLQKqeNXTsx3Hp8XEFh-Q@mail.gmail.com>
Date:   Tue, 24 Aug 2021 22:33:03 +0900
From:   Austin Kim <austindh.kim@...il.com>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        SElinux list <selinux@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        kernel-team@....com, 김동현 <austin.kim@....com>
Subject: Re: [PATCH] selinux: remove duplicated initialization of 'i' for clean-up

2021년 8월 24일 (화) 오후 8:28, Ondrej Mosnacek <omosnace@...hat.com>님이 작성:
>
> Hi Austin,
>
> On Tue, Aug 24, 2021 at 4:23 AM Austin Kim <austindh.kim@...il.com> wrote:
> >
> > From: Austin Kim <austin.kim@....com>
> >
> > The local variable 'i' is used to be incremented inside while loop
> > within sidtab_convert_tree(). Before while loop, 'i' is set to 0
> > inside if/else statement.
> >
> > Since there is no 'goto' statement within sidtab_convert_tree(),
> > it had better initialize 'i' as 0 once before if/else statement.
> >
> > Signed-off-by: Austin Kim <austin.kim@....com>
> > ---
> >  security/selinux/ss/sidtab.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> > index 656d50b09f76..301620de63d3 100644
> > --- a/security/selinux/ss/sidtab.c
> > +++ b/security/selinux/ss/sidtab.c
> > @@ -374,7 +374,7 @@ static int sidtab_convert_tree(union sidtab_entry_inner *edst,
> >                                struct sidtab_convert_params *convert)
> >  {
> >         int rc;
> > -       u32 i;
> > +       u32 i = 0;
> >
> >         if (level != 0) {
> >                 if (!edst->ptr_inner) {
> > @@ -383,7 +383,6 @@ static int sidtab_convert_tree(union sidtab_entry_inner *edst,
> >                         if (!edst->ptr_inner)
> >                                 return -ENOMEM;
> >                 }
> > -               i = 0;
> >                 while (i < SIDTAB_INNER_ENTRIES && *pos < count) {
>
> I must say I prefer the original version more, because it makes it
> clear when you look at the loop that it starts at 0. Once you move the
> initialization to the declaration section, readers will have to scan
> the code upwards to find it out.

Thanks for sharing the full story of the original version.

The original code is more readable since 'i' is mainly used
in 'for' loop rather than 'while' loop. Also agreed that
reader might attempt to scan the initial value of 'i'.

Thanks,
Austin Kim

 As is, it's also less prone to error
> if e.g. someone adds another loop before the existing ones and reuses
> the variable.
>
> In case anyone is wondering why I didn't make these for loops when I
> wrote this code: Since the loop condition a little more than the usual
> "for(i = 0; i < n; i++)" pattern, my intention was to emphasize that
> this is not a "regular" for loop and that readers should read the loop
> carefully to not miss something. But perhaps that's not a good reason
> and they would look more natural as for loops. If others think a for
> loop would look better here, I'd be OK with a patch that makes these
> into for loops instead.
>
> >                         rc = sidtab_convert_tree(&edst->ptr_inner->entries[i],
> >                                                  &esrc->ptr_inner->entries[i],
> > @@ -400,7 +399,6 @@ static int sidtab_convert_tree(union sidtab_entry_inner *edst,
> >                         if (!edst->ptr_leaf)
> >                                 return -ENOMEM;
> >                 }
> > -               i = 0;
> >                 while (i < SIDTAB_LEAF_ENTRIES && *pos < count) {
> >                         rc = convert->func(&esrc->ptr_leaf->entries[i].context,
> >                                            &edst->ptr_leaf->entries[i].context,
> > --
> > 2.20.1
> >
>
> --
> Ondrej Mosnacek
> Software Engineer, Linux Security - SELinux kernel
> Red Hat, Inc.
>