linux-kernel - Re: [PATCH v4 3/4] net/sched: Load modules via their alias

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Date: Tue, 23 Jan 2024 17:40:02 +0000
From: Simon Horman <horms@...nel.org>
To: Michal Koutný <mkoutny@...e.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org, cake@...ts.bufferbloat.net,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Petr Pavlu <ppavlu@...e.cz>, Michal Kubecek <mkubecek@...e.cz>,
	Martin Wilck <mwilck@...e.com>,
	Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH v4 3/4] net/sched: Load modules via their alias

On Tue, Jan 23, 2024 at 02:52:41PM +0100, Michal Koutný wrote:
> The cls_,sch_,act_ modules may be loaded lazily during network
> configuration but without user's awareness and control.
> 
> Switch the lazy loading from canonical module names to a module alias.
> This allows finer control over lazy loading, the precedent from
> commit 7f78e0351394 ("fs: Limit sys_mount to only request filesystem
> modules.") explains it already:
> 
> 	Using aliases means user space can control the policy of which
> 	filesystem^W net/sched modules are auto-loaded by editing
> 	/etc/modprobe.d/*.conf with blacklist and alias directives.
> 	Allowing simple, safe, well understood work-arounds to known
> 	problematic software.
> 
> By default, nothing changes. However, if a specific module is
> blacklisted (its canonical name), it won't be modprobe'd when requested
> under its alias (i.e. kernel auto-loading). It would appear as if the
> given module was unknown.
> 
> The module can still be loaded under its canonical name, which is an
> explicit (privileged) user action.
> 
> Signed-off-by: Michal Koutný <mkoutny@...e.com>
> ---
>  net/sched/act_api.c | 2 +-
>  net/sched/cls_api.c | 2 +-
>  net/sched/sch_api.c | 4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index 3e30d7260493..60c0fadfac6d 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -1363,7 +1363,7 @@ struct tc_action_ops *tc_action_load_ops(struct nlattr *nla, u32 flags,
>  
>  		if (rtnl_held)
>  			rtnl_unlock();
> -		request_module("act_%s", act_name);
> +		request_module(NET_ACT_ALIAS_PREFIX "%s", name);

Hi Michal,

name doesn't exist in this context, perhaps the line above should be:

		request_module(NET_ACT_ALIAS_PREFIX "%s", act_name);

>  		if (rtnl_held)
>  			rtnl_lock();
>  
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 92a12e3d0fe6..b31b832598e7 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -257,7 +257,7 @@ tcf_proto_lookup_ops(const char *kind, bool rtnl_held,
>  #ifdef CONFIG_MODULES
>  	if (rtnl_held)
>  		rtnl_unlock();
> -	request_module("cls_%s", kind);
> +	request_module(NET_CLS_ALIAS_PREFIX "%s", name);

Likewise, perhaps the line above should be:

	request_module(NET_CLS_ALIAS_PREFIX "%s", kind);

>  	if (rtnl_held)
>  		rtnl_lock();
>  	ops = __tcf_proto_lookup_ops(kind);

..

-- 
pw-bot: changes-requested