linux-kernel - Re: [PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL

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Message-ID: <ZMgbyNKnotCMyB+f@bombadil.infradead.org>
Date:   Mon, 31 Jul 2023 13:38:32 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Yangbo Lu <yangbo.lu@....com>,
        Joshua Kinard <kumba@...too.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-arm-kernel@...ts.infradead.org,
        open list <linux-kernel@...r.kernel.org>,
        linux-mmc@...r.kernel.org, netdev@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-modules@...r.kernel.org
Subject: Re: [PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL_GPL
 modules

On Mon, Jul 31, 2023 at 10:38:06AM +0200, Christoph Hellwig wrote:
> ---
>  kernel/module/internal.h |  1 +
>  kernel/module/main.c     | 17 ++++++++++++-----
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/module/internal.h b/kernel/module/internal.h
> index c8b7b4dcf7820d..add687c2abde8b 100644
> --- a/kernel/module/internal.h
> +++ b/kernel/module/internal.h
> @@ -93,6 +93,7 @@ struct find_symbol_arg {
>  	/* Input */
>  	const char *name;
>  	bool gplok;
> +	bool gplonly;

We'd want to add here a reason or something like that to allow the
caller to know why we failed if we want to provide feedback.

>  	bool warn;
>  
>  	/* Output */
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 59b1d067e52890..85d3f00ca65758 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -281,6 +281,8 @@ static bool find_exported_symbol_in_section(const struct symsearch *syms,
>  
>  	if (!fsa->gplok && syms->license == GPL_ONLY)
>  		return false;
> +	if (fsa->gplonly && syms->license != GPL_ONLY)

And set it here to something other than perhaps a default of NOT_FOUND.

> +		return false;
>  
>  	sym = bsearch(fsa->name, syms->start, syms->stop - syms->start,
>  			sizeof(struct kernel_symbol), cmp_name);
> @@ -776,8 +778,9 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> @@ -1289,14 +1292,18 @@ static void free_module(struct module *mod)
>  void *__symbol_get(const char *symbol)
>  {
>  	struct find_symbol_arg fsa = {
> -		.name	= symbol,
> -		.gplok	= true,
> -		.warn	= true,
> +		.name		= symbol,
> +		.gplok		= true,
> +		.gplonly	= true,
> +		.warn		= true,
>  	};
>  
>  	preempt_disable();
>  	if (!find_symbol(&fsa) || strong_try_module_get(fsa.owner)) {
>  		preempt_enable();
> +		if (fsa.gplonly)
> +			pr_warn("failing symbol_get of non-GPLONLY symbol %s.\n",

Because here fsa.gplonly is always true here so the above warn will
print even if a symbol is just not found.

  Luis