linux-kernel - Re: [PATCH] module: report -EFAULT on bytes remaining

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Date:	Wed, 12 Sep 2012 18:40:23 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Fengguang Wu <fengguang.wu@...el.com>,
	kernel-janitors@...r.kernel.org,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] module: report -EFAULT on bytes remaining

On Wed, Sep 12, 2012 at 08:06:16AM -0700, Kees Cook wrote:
> Caught by smatch:
> kernel/module.c:2450 copy_module_from_user() warn: maybe return -EFAULT instead of the bytes remaining?  
> 
> Clean up the copy_from_user() call to not report a positive value.
> With this patch, init_module() will report errors from copy_from_user
> (before it would always only report -EFAULT when err != 0).
> 
> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> This change is on top of the finit_module patch series.
> ---
>  kernel/module.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 0ad03c4..05b8dde 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2441,8 +2441,11 @@ int copy_module_from_user(const void __user *umod, unsigned long len,
>  		return -ENOMEM;
>  
>  	err = copy_from_user(info->hdr, umod, info->len);
> -	if (err)
> +	if (err) {
> +		if (err > 0)
                ^^^^^^^^^^^
This condition is always true because copy_to/from_user() returns
the number of bytes remaining to be copied.  (It never returns a
negative error code).

> +			err = -EFAULT;
>  		goto free_hdr;
> +	}

regards,
dan carpenter


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