linux-kernel - Re: [PATCH v3] Add kernel parameter to blacklist modules

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Date:	Mon, 18 Jul 2016 13:03:58 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Prarit Bhargava <prarit@...hat.com>, linux-kernel@...r.kernel.org
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3] Add kernel parameter to blacklist modules

Prarit Bhargava <prarit@...hat.com> writes:
> Blacklisting a module in linux has long been a problem.  The current
> procedure is to use rd.blacklist=module_name, however, that doesn't
> cover the case after the initramfs and before a boot prompt (where one
> is supposed to use /etc/modprobe.d/blacklist.conf to blacklist
> runtime loading). Using rd.shell to get an early prompt is hit-or-miss,
> and doesn't cover all situations AFAICT.
>
> This patch adds this functionality of permanently blacklisting a module
> by its name via the kernel parameter module_blacklist=module_name.
>
> [v2]: Rusty, use core_param() instead of __setup() which simplifies
> things.
>
> [v3]: Rusty, undo wreckage from strsep()

There's no locking here, meaning that something can easily slip through
the blacklist.

This time for sure! (UNTESTED!)

static bool blacklisted(char *module_name)
{
	const char *p;
        size_t len;

	if (!module_blacklist)
		return false;

        for (p = module_blacklist; *p; p += len) {
                len = strcspn(p, ",");
                if (strlen(module_name) == len && !memcmp(module_name, p, len))
                        return true;
                if (p[len] == ',')
                        len++;
        }
        return false;
}

Thanks,
Rusty.

>
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: linux-doc@...r.kernel.org
> ---
>  Documentation/kernel-parameters.txt |    3 +++
>  kernel/module.c                     |   29 +++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 82b42c958d1c..c720b96f2efc 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2295,6 +2295,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			Note that if CONFIG_MODULE_SIG_FORCE is set, that
>  			is always true, so this option does nothing.
>  
> +	module_blacklist=  [KNL] Do not load a comma-separated list of
> +			modules.  Useful for debugging problem modules.
> +
>  	mousedev.tap_time=
>  			[MOUSE] Maximum time between finger touching and
>  			leaving touchpad surface for touch to be considered
> diff --git a/kernel/module.c b/kernel/module.c
> index 5f71aa63ed2a..5240da88af79 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3155,6 +3155,32 @@ int __weak module_frob_arch_sections(Elf_Ehdr *hdr,
>  	return 0;
>  }
>  
> +/* module_blacklist is a comma-separated list of module names */
> +static char *module_blacklist;
> +static bool blacklisted(char *module_name)
> +{
> +	char *str, *entry;
> +
> +	if (!module_blacklist)
> +		return false;
> +
> +	str = module_blacklist;
> +	do {
> +		if (str != module_blacklist)
> +			module_blacklist[strlen(str) - 1] = ',';
> +		entry = strsep(&str, ",");
> +		if (!strcmp(module_name, entry)) {
> +			pr_info("module %s is blacklisted\n", module_name);
> +			if (str != module_blacklist)
> +				module_blacklist[strlen(str) - 1] = ',';
> +			return true;
> +		}
> +	} while (str);
> +
> +	return false;
> +}
> +core_param(module_blacklist, module_blacklist, charp, 0400);
> +
>  static struct module *layout_and_allocate(struct load_info *info, int flags)
>  {
>  	/* Module within temporary copy. */
> @@ -3165,6 +3191,9 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
>  	if (IS_ERR(mod))
>  		return mod;
>  
> +	if (blacklisted(mod->name))
> +		return ERR_PTR(-EPERM);
> +
>  	err = check_modinfo(mod, info, flags);
>  	if (err)
>  		return ERR_PTR(err);
> -- 
> 1.7.9.3