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Date: Wed, 2 Nov 2016 19:16:41 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Jann Horn <jann@thejh.net>
Cc: Seth Forshee <seth.forshee@canonical.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Doug Ledford <dledford@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Tejun Heo <tj@kernel.org>, Roland McGrath <roland@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] signal: fix overflow_uid signal sender
Message-ID: <20161102181640.GA1112@redhat.com>
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On 10/31, Jann Horn wrote:
>
>  static inline void userns_fixup_signal_uid(struct siginfo *info, struct task_struct *t)
>  {
> -	if (current_user_ns() == task_cred_xxx(t, user_ns))
> +	if (&init_user_ns == task_cred_xxx(t, user_ns))
>  		return;
>  
>  	if (SI_FROMKERNEL(info))
> @@ -959,7 +959,7 @@ static inline void userns_fixup_signal_uid(struct siginfo *info, struct task_str
>  
>  	rcu_read_lock();
>  	info->si_uid = from_kuid_munged(task_cred_xxx(t, user_ns),
> -					make_kuid(current_user_ns(), info->si_uid));
> +					make_kuid(&init_user_ns, info->si_uid));
>  	rcu_read_unlock();
>  }
>  #else
> @@ -1027,7 +1027,8 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
>  			q->info.si_code = SI_USER;
>  			q->info.si_pid = task_tgid_nr_ns(current,
>  							task_active_pid_ns(t));
> -			q->info.si_uid = from_kuid_munged(current_user_ns(), current_uid());
> +			q->info.si_uid = from_kuid(&init_user_ns,
> +						   current_uid());

Looks good to me at first glance, but I think this needs an ack from Eric.

I have to admit that I forgot how uid_map/etc actually works, I can't
even recall if from_kuid(init_user_ns, xxx) == __kuid_val(xxx) or not,
although this doesn't really matter.

Oleg.