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Date:   Thu, 4 Jul 2019 21:50:25 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jann Horn <jannh@...gle.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [RFC PATCH] binfmt_elf: Extract .note.gnu.property from an ELF
 file

Hi!


> > +static int scan(u8 *buf, u32 buf_size, int item_size, test_item_fn test_item,
> > +               next_item_fn next_item, u32 *arg, u32 type, u32 *pos)
> > +{
> > +       int found = 0;
> > +       u8 *p, *max;
> > +
> > +       max = buf + buf_size;
> > +       if (max < buf)
> > +               return 0;
> 
> How can this ever legitimately happen? If it can't, perhaps you meant
> to put a WARN_ON_ONCE() or something like that here?
> Also, computing out-of-bounds pointers is UB (section 6.5.6 of C99:
> "If both the pointer operand and the result point to elements of the
> same array object, or one past the last element of the array object,
> the evaluation shall not produce an overflow; otherwise, the behavior
> is undefined."), and if the addition makes the pointer wrap, that's
> certainly out of bounds; so I don't think this condition can trigger
> without UB.

Kernel assumes sane compiler. We pass flags to get it... C99 does not
quite apply here.
								Pavel
								
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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