linux-kernel - Re: [PATCH 6/7] pipe: simplify round_pipe

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Message-ID: <20180110025201.GC931@zzz.localdomain>
Date:   Tue, 9 Jan 2018 18:52:01 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Willy Tarreau <w@....eu>,
        Mikulas Patocka <mpatocka@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH 6/7] pipe: simplify round_pipe_size()

On Tue, Jan 09, 2018 at 02:27:10PM -0800, Kees Cook wrote:
> 
> > @@ -1054,9 +1048,6 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
> >                 return -EINVAL;
> >         nr_pages = size >> PAGE_SHIFT;
> >
> > -       if (!nr_pages)
> > -               return -EINVAL;
> > -
> 
> I would just leave this hunk anyway: it's defensive for any future
> changes. Maybe add a comment describing why it's currently redundant?
> 

I don't know; I find it really confusing to have two slightly different checks
for the same thing, as it implies that they actually need to be there for a
reason.  How about just checking nr_pages?

        size = round_pipe_size(arg);
        nr_pages = size >> PAGE_SHIFT;

        if (nr_pages == 0)
                return -EINVAL;

Eric