linux-kernel - Re: [PATCH] uaccess: Disallow > INT

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Message-ID: <201909231607.B6A0736@keescook>
Date:   Mon, 23 Sep 2019 16:08:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uaccess: Disallow > INT_MAX copy sizes

On Sun, Aug 25, 2019 at 04:18:56PM -0700, Kees Cook wrote:
> As we've done with VFS, string operations, etc, reject usercopy sizes
> larger than INT_MAX, which would be nice to have for catching bugs
> related to size calculation overflows[1].
> 
> This adds 10 bytes to x86_64 defconfig text and 1980 bytes to the data
> section:
> 
>    text    data     bss     dec     hex filename
> 19691167        5134320 1646664 26472151        193eed7 vmlinux.before
> 19691177        5136300 1646664 26474141        193f69d vmlinux.after
> 
> [1] https://marc.info/?l=linux-s390&m=156631939010493&w=2
> 
> Suggested-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

ping! Andrew, can you take this?

-Kees

> ---
>  include/linux/thread_info.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 659a4400517b..e93e249a4e9b 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -147,6 +147,8 @@ check_copy_size(const void *addr, size_t bytes, bool is_source)
>  			__bad_copy_to();
>  		return false;
>  	}
> +	if (WARN_ON_ONCE(bytes > INT_MAX))
> +		return false;
>  	check_object_size(addr, bytes, is_source);
>  	return true;
>  }
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook

-- 
Kees Cook