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From: Alexey Dobriyan <adobriyan@gmail.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] elf: don't be afraid of overflow
Date: Mon, 11 Mar 2019 20:10:06 +0300	[thread overview]
Message-ID: <20190311171006.GA2141@avx2> (raw)
In-Reply-To: <20190311110423.GC14118@amd>

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.

> > @@ -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.

	size = sizeof(struct elf_phdr) * elf_ex->e_phnum;
        if (size == 0 || size > 65536 || size > ELF_MIN_ALIGN)
                goto out;

  reply	other threads:[~2019-03-11 17:10 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-04 20:27 Alexey Dobriyan
2019-02-04 20:28 ` [PATCH 2/4] elf: use list_for_each_entry() Alexey Dobriyan
2019-02-04 20:28   ` [PATCH 3/4] elf: spread const a little Alexey Dobriyan
2019-02-04 20:33     ` [PATCH 4/4] elf: save allocation per exec Alexey Dobriyan
2019-02-12 15:49   ` [PATCH 2/4] elf: use list_for_each_entry() kbuild test robot
2019-02-12 16:21   ` kbuild test robot
2019-03-11 11:04 ` [PATCH 1/4] elf: don't be afraid of overflow Pavel Machek
2019-03-11 17:10   ` Alexey Dobriyan [this message]
2019-03-12  9:37     ` Pavel Machek

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