[PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL_GPL modules

[Luis Chamberlain]

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