linux-kernel - Re: [PATCH] module: check vermagic match exactly when load modules

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Date:	Thu, 10 Dec 2015 13:36:12 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Xie XiuQi <xiexiuqi@...wei.com>, paulmck@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org, bobby.prani@...il.com
Cc:	dhowells@...hat.com, David.Woodhouse@...el.com,
	linux-kernel@...r.kernel.org, hannes@...xchg.org,
	iulia.manda21@...il.com, luto@...capital.net,
	huawei.libin@...wei.com
Subject: Re: [PATCH] module: check vermagic match exactly when load modules

Xie XiuQi <xiexiuqi@...wei.com> writes:
> Usually, checking kernel version will be ignore when loading
> modules if CONFIG_MODVERSIONS option is enable. This could
> potentially lead to a mismatch with the running kernel.
>
> With this option, we prevent to load the modules which vermagic
> is not match exactly with the running kernel.
>
> It could be set to N by default.

Hi Xie!

        I don't understand this patch.  The purpose of
CONFIG_MODVERSIONS is so that you can combine modules from different
kernel versions.  If you don't want to do that, I suggest not setting
CONFIG_MODVERSIONS.

Cheers,
Rusty.

>
> Signed-off-by: Xie XiuQi <xiexiuqi@...wei.com>
> ---
>  init/Kconfig    | 11 +++++++++++
>  kernel/module.c |  2 ++
>  2 files changed, 13 insertions(+)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index c24b6f7..ce9c23e 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1889,6 +1889,17 @@ config MODVERSIONS
>  	  make them incompatible with the kernel you are running.  If
>  	  unsure, say N.
>  
> +config MODULE_VERMAGIC_FORCE
> +	bool "Require vermagic match exactly"
> +	default n
> +	depends on MODVERSIONS
> +	help
> +	  Usually, checking kernel version will be ignore when loading
> +	  modules if CONFIG_MODVERSIONS option is enable. This could
> +	  potentially lead to a mismatch with the running kernel.
> +	  With this option, we prevent to load the modules which vermagic
> +	  is not match exactly with the running kernel. If unsure, say N.
> +
>  config MODULE_SRCVERSION_ALL
>  	bool "Source checksum for all modules"
>  	help
> diff --git a/kernel/module.c b/kernel/module.c
> index 8f051a1..cf350d5 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1350,10 +1350,12 @@ static inline int check_modstruct_version(Elf_Shdr *sechdrs,
>  static inline int same_magic(const char *amagic, const char *bmagic,
>  			     bool has_crcs)
>  {
> +#ifndef CONFIG_MODULE_VERMAGIC_FORCE
>  	if (has_crcs) {
>  		amagic += strcspn(amagic, " ");
>  		bmagic += strcspn(bmagic, " ");
>  	}
> +#endif
>  	return strcmp(amagic, bmagic) == 0;
>  }
>  #else
> -- 
> 1.8.3.1
>
> --
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