linux-kernel - Re: [PATCH 1/4] elf: don't be afraid of overflow

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Message-ID: <20190312093754.GB28905@amd>
Date:   Tue, 12 Mar 2019 10:37:54 +0100
From:   Pavel Machek <pavel@....cz>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] elf: don't be afraid of overflow

On Mon 2019-03-11 20:10:06, Alexey Dobriyan wrote:
> On Mon, Mar 11, 2019 at 12:04:23PM +0100, Pavel Machek wrote:
> > On Mon 2019-02-04 23:27:15, Alexey Dobriyan wrote:
> > > Number of ELF program headers is 16-bit by spec, so total size
> > > comfortably fits into "unsigned int".
> > 
> > If it can't overflow, gcc should know too, and optimize checks
> > out... right?
> 
> Turns out it doesn't.

Tells me you are doing something wrong.

> > > @@ -429,13 +430,9 @@ static struct elf_phdr *load_elf_phdrs(struct elfhdr *elf_ex,
> > >  		goto out;
> > >  
> > >  	/* Sanity check the number of program headers... */
> > > -	if (elf_ex->e_phnum < 1 ||
> > > -		elf_ex->e_phnum > 65536U / sizeof(struct elf_phdr))
> > > -		goto out;
> > > -
> > >  	/* ...and their total size. */
> > 
> > This is just wrong. You removed check for zero, and I'm pretty sure
> > sizeof() is not 1, so this one can trigger, too.
> 
> No. ->e_phnum is 65535 max.

That does not invalidate my argument.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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