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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     davem@davemloft.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, avagin@virtuozzo.com,
        ktkhai@virtuozzo.com, serge@hallyn.com, gregkh@linuxfoundation.org
References: <20180428192025.2075-1-christian.brauner@ubuntu.com>
        <20180428192025.2075-3-christian.brauner@ubuntu.com>
Date:   Sat, 28 Apr 2018 23:23:58 -0500
In-Reply-To: <20180428192025.2075-3-christian.brauner@ubuntu.com> (Christian
        Brauner's message of "Sat, 28 Apr 2018 21:20:25 +0200")
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Subject: Re: [PATCH net-next 2/2 v4] netns: restrict uevents
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> +	/* fix credentials */
> +	if (owning_user_ns != &init_user_ns) {
> +		struct netlink_skb_parms *parms = &NETLINK_CB(skb);
> +		kuid_t root_uid;
> +		kgid_t root_gid;
> +
> +		/* fix uid */
> +		root_uid = make_kuid(owning_user_ns, 0);
> +		if (!uid_valid(root_uid))
> +			root_uid = GLOBAL_ROOT_UID;
> +		parms->creds.uid = root_uid;
> +
> +		/* fix gid */
> +		root_gid = make_kgid(owning_user_ns, 0);
> +		if (!gid_valid(root_gid))
> +			root_gid = GLOBAL_ROOT_GID;
> +		parms->creds.gid = root_gid;

One last nit:

	You can only make the assignment if the uid is valid.
        Leaving it GLBOAL_ROOT_UID if the composed uid is invalid.
        AKA

		/* fix uid */
		root_uid = make_kuid(owning_user_ns, 0);
		if (uid_valid(root_uid))
                	parms->creds.uid = root_uid;

                /* fix gid */
		root_gid = make_kgid(owning_user_ns, 0);
                if (gid_valid(root_gid))
                	params->creds.gid = root_gid;


One line shorter and I think a little clearer.  I suspect
it even results in better code.

Eric