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

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Message-ID: <20190311110423.GC14118@amd>
Date:   Mon, 11 Mar 2019 12:04:23 +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 2019-02-04 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?

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

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