netdev - Re: [PATCH 7/9] net: centralize ns

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Message-ID: <kiyr4pnrw2a2oeoc3lavj73glvdg5llsfz2txfnn56bxmytfgw@o6weansm3iyi>
Date: Thu, 18 Sep 2025 11:42:38 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, Amir Goldstein <amir73il@...il.com>, 
	Josef Bacik <josef@...icpanda.com>, Jeff Layton <jlayton@...nel.org>, Mike Yuan <me@...dnzj.com>, 
	Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, Lennart Poettering <mzxreary@...inter.de>, 
	Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Koutný <mkoutny@...e.com>, 
	Jakub Kicinski <kuba@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 7/9] net: centralize ns_common initialization

On Wed 17-09-25 12:28:06, Christian Brauner wrote:
> Centralize ns_common initialization.
> 
> Signed-off-by: Christian Brauner <brauner@...nel.org>
> ---
>  net/core/net_namespace.c | 23 +++--------------------
>  1 file changed, 3 insertions(+), 20 deletions(-)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index a57b3cda8dbc..897f4927df9e 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -409,7 +409,7 @@ static __net_init int preinit_net(struct net *net, struct user_namespace *user_n
>  	ns_ops = NULL;
>  #endif
>  
> -	ret = ns_common_init(&net->ns, ns_ops, false);
> +	ret = ns_common_init(&net->ns, ns_ops, true);
>  	if (ret)
>  		return ret;
>  
> @@ -597,6 +597,7 @@ struct net *copy_net_ns(unsigned long flags,
>  		net_passive_dec(net);
>  dec_ucounts:
>  		dec_net_namespaces(ucounts);
> +		ns_free_inum(&net->ns);

This looks like a wrong place to put it? dec_ucounts also gets called when we
failed to create 'net' and thus net == NULL. 

>  		return ERR_PTR(rv);
>  	}
>  	return net;
> @@ -718,6 +719,7 @@ static void cleanup_net(struct work_struct *work)
>  #endif
>  		put_user_ns(net->user_ns);
>  		net_passive_dec(net);
> +		ns_free_inum(&net->ns);

The calling of ns_free_inum() after we've dropped our reference
(net_passive_dec()) looks suspicious. Given how 'net' freeing works I don't
think this can lead to actual UAF issues but it is in my opinion a bad
coding pattern and for no good reason AFAICT.

>  	}
>  	WRITE_ONCE(cleanup_net_task, NULL);
>  }

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR