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Date: Tue, 28 Oct 2025 10:30:06 +0000
From: Simon Horman <horms@kernel.org>
To: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, Josef Bacik <josef@toxicpanda.com>,
	Jeff Layton <jlayton@kernel.org>, Jann Horn <jannh@google.com>,
	Mike Yuan <me@yhndnzj.com>,
	Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>,
	Lennart Poettering <mzxreary@0pointer.de>,
	Daan De Meyer <daan.j.demeyer@gmail.com>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Amir Goldstein <amir73il@gmail.com>, Tejun Heo <tj@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	bpf@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v3 11/70] ns: add active reference count
Message-ID: <aQCbLrYf_KTdxZjU@horms.kernel.org>
References: <20251024-work-namespace-nstree-listns-v3-0-b6241981b72b@kernel.org>
 <20251024-work-namespace-nstree-listns-v3-11-b6241981b72b@kernel.org>
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In-Reply-To: <20251024-work-namespace-nstree-listns-v3-11-b6241981b72b@kernel.org>

On Fri, Oct 24, 2025 at 12:52:40PM +0200, Christian Brauner wrote:

...

> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c

...

> +void get_cred_namespaces(struct task_struct *tsk)
> +{
> +	ns_ref_active_get(tsk->real_cred->user_ns);

Hi Christian,

real_cred is protected by RCU, but this code doesn't seem to take
that into account. Or, at least Sparse doesn't think so:

.../nsproxy.c:264:9: error: no generic selection for 'struct user_namespace *const [noderef] __rcu user_ns'
.../nsproxy.c:264:9: warning: dereference of noderef expression

> +}
> +
> +void exit_cred_namespaces(struct task_struct *tsk)
> +{
> +	ns_ref_active_put(tsk->real_cred->user_ns);

Likewise here.

> +}
> +
>  int exec_task_namespaces(void)
>  {
>  	struct task_struct *tsk = current;

...