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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190311171006.GA2141@avx2>
Date:   Mon, 11 Mar 2019 20:10:06 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] elf: don't be afraid of overflow

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;