Re: [PATCH] libkmod: introduce kmod_module_uniq_options() to improve the reliability of loading module

[Alexey Gladkov <gladkov.alexey@gmail.com>]

On Wed, Apr 29, 2020 at 11:52:08PM +0800, Wen Yang wrote:
> As in commit 2045cdfa1b40 ("netfilter: nf_conntrack: Fix possible possible crash on module loading"),
> Loading the nf_conntrack module with doubled hashsize parameter, i.e.
> 	  modprobe nf_conntrack hashsize=12345 hashsize=12345
> causes NULL-ptr deref.
> 
> If 'hashsize' specified twice, the nf_conntrack_set_hashsize() function
> will be called also twice.
> 
> In addition, we may also construct the doubled hashsize parameter scenario by using the following configuration:
> 
> $ cat /etc/modprobe.d/firewalld-sysctls.conf
> install nf_conntrack /usr/sbin/modprobe --ignore-install nf_conntrack $CMDLINE_OPTS && /usr/sbin/sysctl --quiet --pattern 'net[.]netfilter[.]nf_conntrack.*' --system
> 
> $ cat /etc/modprobe.d/nf_conntrack.conf
> options nf_conntrack hashsize=187600
> 
> $ sudo modprobe nf_conntrack -v
> install /usr/sbin/modprobe --ignore-install nf_conntrack $CMDLINE_OPTS && /usr/sbin/sysctl --quiet --pattern 'net[.]netfilter[.]nf_conntrack.*' --system hashsize=187500
> insmod /path/to/nf_conntrack.ko hashsize=187500 hashsize=187500
> 
> Passing multiple repeated parameters to the kernel may trigger kernel bugs
> and affect the performance of loading kernel modules.
> 
> We introduce the nf_conntrack_set_hashsize() and hope to solve this problem.
> 
> Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: Lucas De Marchi <lucas.de.marchi@gmail.com>
> Cc: Topi Miettinen <toiwoton@gmail.com>
> Cc: Alexey Gladkov <gladkov.alexey@gmail.com>
> Cc: linux-modules@vger.kernel.org
> ---
>  libkmod/libkmod-module.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++
>  libkmod/libkmod.h        |  1 +
>  tools/insmod.c           |  7 +++++
>  3 files changed, 80 insertions(+)
> 
> diff --git a/libkmod/libkmod-module.c b/libkmod/libkmod-module.c
> index 76a6dc3..f42beb8 100644
> --- a/libkmod/libkmod-module.c
> +++ b/libkmod/libkmod-module.c
> @@ -1076,6 +1076,72 @@ static char *module_options_concat(const char *opt, const char *xopt)
>  	return r;
>  }
>  
> +static unsigned int module_options_cnt(const char *opts)
> +{
> +	int nr_opts = 0;
> +	char *saveptr, *tok, *buf;
> +
> +	if (!opts)
> +		return 0;
> +
> +	buf = strdup(opts);
> +	for (tok = strtok_r(buf, " ", &saveptr); tok != NULL;

Why not use strchr() to find the " " and count them ?

> +	     tok = strtok_r(NULL, " ", &saveptr), nr_opts++) {}
> +

Parameters can have spaces [1]. Is not it so ?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/cmdline.c#n196

> +	free(buf);
> +	return nr_opts;
> +}
> +
> +KMOD_EXPORT int kmod_module_uniq_options(char **opts)
> +{
> +	char *buf;
> +	char **array;
> +	bool duplicated;
> +	char *saveptr, *tok;
> +	int nr_opts, len, i, j;
> +
> +	if (!opts || !*opts)
> +		return 0;
> +
> +	buf = strdup(*opts);

We have the options passed as an argument. You doubled it here and tripled
in the module_options_cnt(). Can you reduce memory usage ?

> +	if (!buf)
> +		return  -ENOMEM;
> +
> +	len = strlen(buf);
> +	nr_opts = module_options_cnt(buf);
> +	array = calloc(nr_opts, sizeof(char *));
> +	if (!buf)
> +		return  -ENOMEM;
> +
> +	for (tok = strtok_r(buf, " ", &saveptr), i = 0; tok != NULL;
> +			tok = strtok_r(NULL, " ", &saveptr), i++) {
> +		array[i] = tok;
> +	}
> +
> +	(*opts)[0] = '\0';
> +	len = 0;
> +	for (i = 0; i < nr_opts; i++) {
> +		duplicated = false;
> +		for (j = 0; j < i; j++) {
> +			if (strcmp(array[i], array[j]) == 0) {
> +				duplicated = true;
> +				break;
> +			}
> +		}
> +
> +		if (!duplicated) {
> +			strcat(*opts, array[i]);
> +			strcat(*opts, " ");
> +			len += strlen(array[i]) + 1;
> +		}
> +	}
> +
> +	(*opts)[len] = '\0';
> +	free(buf);
> +	free(array);
> +	return 0;
> +}
> +
>  static int __kmod_module_get_probe_list(struct kmod_module *mod,
>  						bool required,
>  						bool ignorecmd,
> @@ -1322,6 +1388,12 @@ KMOD_EXPORT int kmod_module_probe_insert_module(struct kmod_module *mod,
>  		options = module_options_concat(moptions,
>  					m == mod ? extra_options : NULL);
>  
> +		err = kmod_module_uniq_options(&options);
> +		if (err < 0) {
> +			free(options);
> +			return err;
> +		}
> +
>  		if (cmd != NULL && !m->ignorecmd) {
>  			if (print_action != NULL)
>  				print_action(m, true, options ?: "");
> diff --git a/libkmod/libkmod.h b/libkmod/libkmod.h
> index 3cab2e5..774e52a 100644
> --- a/libkmod/libkmod.h
> +++ b/libkmod/libkmod.h
> @@ -186,6 +186,7 @@ int kmod_module_probe_insert_module(struct kmod_module *mod,
>  const char *kmod_module_get_name(const struct kmod_module *mod);
>  const char *kmod_module_get_path(const struct kmod_module *mod);
>  const char *kmod_module_get_options(const struct kmod_module *mod);
> +int kmod_module_uniq_options(char **opts);
>  const char *kmod_module_get_install_commands(const struct kmod_module *mod);
>  const char *kmod_module_get_remove_commands(const struct kmod_module *mod);
>  struct kmod_list *kmod_module_get_dependencies(const struct kmod_module *mod);
> diff --git a/tools/insmod.c b/tools/insmod.c
> index c422971..2dc0c22 100644
> --- a/tools/insmod.c
> +++ b/tools/insmod.c
> @@ -132,6 +132,13 @@ static int do_insmod(int argc, char *argv[])
>  		opts[optslen] = '\0';
>  	}
>  
> +	err = kmod_module_uniq_options(&opts);
> +	if (err < 0) {
> +		ERR("kmod_module_uniq_options() failed!\n");
> +		free(opts);
> +		return err;
> +	}
> +
>  	ctx = kmod_new(NULL, &null_config);
>  	if (!ctx) {
>  		ERR("kmod_new() failed!\n");
> -- 
> 1.8.3.1
> 

-- 
Rgrds, legion