linux-kernel - Re: [PATCH 04/12] module: move early sanity checks into a helper

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Date:   Fri, 24 Mar 2023 14:02:06 +0100
From:   Petr Pavlu <petr.pavlu@...e.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     christophe.leroy@...roup.eu, song@...nel.org,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
        pmladek@...e.com, david@...hat.com, prarit@...hat.com
Subject: Re: [PATCH 04/12] module: move early sanity checks into a helper

On 3/19/23 22:27, Luis Chamberlain wrote:
> Move early sanity checkers for the module into a helper.
> This let's us make it clear when we are working with the
> local copy of the module prior to allocation.
> 
> This produces no functional changes, it just makes subsequent
> changes easier to read.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  kernel/module/main.c | 43 ++++++++++++++++++++++++++-----------------
>  1 file changed, 26 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 427284ab31f1..933cef72ae13 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -2668,6 +2668,31 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname,
>  	return 0;
>  }
>  
> +/* Module within temporary copy, this doesn't do any allocation  */
> +static int early_mod_check(struct load_info *info, int flags)
> +{
> +	int err;
> +
> +	/*
> +	 * Now that we know we have the correct module name, check
> +	 * if it's blacklisted.
> +	 */
> +	if (blacklisted(info->name)) {
> +		pr_err("Module %s is blacklisted\n", info->name);
> +		return -EPERM;
> +	}
> +
> +	err = rewrite_section_headers(info, flags);
> +	if (err)
> +		return err;
> +
> +	/* Check module struct version now, before we try to use module. */
> +	if (!check_modstruct_version(info, info->mod))
> +		return ENOEXEC;

The error value when check_modstruct_version() fails is changed in this patch
from -ENOEXEC to ENOEXEC and updated back again in the next patch. It would be
good to avoid introducing this temporary problem and keep the value throughout
as -ENOEXEC.

> +
> +	return 0;
> +}
> +
>  /*
>   * Allocate and load the module: note that size of section 0 is always
>   * zero, and we rely on this for optional sections.
> @@ -2711,26 +2736,10 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  	if (err)
>  		goto free_copy;
>  
> -	/*
> -	 * Now that we know we have the correct module name, check
> -	 * if it's blacklisted.
> -	 */
> -	if (blacklisted(info->name)) {
> -		err = -EPERM;
> -		pr_err("Module %s is blacklisted\n", info->name);
> -		goto free_copy;
> -	}
> -
> -	err = rewrite_section_headers(info, flags);
> +	err = early_mod_check(info, flags);
>  	if (err)
>  		goto free_copy;
>  
> -	/* Check module struct version now, before we try to use module. */
> -	if (!check_modstruct_version(info, info->mod)) {
> -		err = -ENOEXEC;

Original value here.

> -		goto free_copy;
> -	}
> -
>  	/* Figure out module layout, and allocate all the memory. */
>  	mod = layout_and_allocate(info, flags);
>  	if (IS_ERR(mod)) {

Thanks,
Petr