linux-kernel - Re: [PATCH v6] pidns: introduce syscall translate

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Message-ID: <c877358b-b7eb-c019-691e-fec489329f88@oracle.com>
Date:   Mon, 23 Jul 2018 14:13:37 -0700
From:   Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>
To:     Michael Tirado <mtirado418@...il.com>
Cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        linux-api@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>,
        Serge Hallyn <serge.hallyn@...ntu.com>,
        Prakash Sangappa <prakash.sangappa@...cle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH v6] pidns: introduce syscall translate_pid



On 07/23/2018 01:55 PM, Michael Tirado wrote:
> Hey, I'm not seeing much activity on this so here's my $0.02
>
>> Unix socket automatically translates pid attached to SCM_CREDENTIALS.
>> This requires CAP_SYS_ADMIN for sending arbitrary pids and entering
>> into pid namespace, this expose process and could be insecure.
>
> Perhaps it would be a good idea to add a sysctl switch that prevents
> credential spoofing over AF_UNIX \by default\ if that is the main
> concern, or is there another concern and I have read this wrong?  I'm
> having trouble thinking of a legitimate use of SCM_CREDENTIALS
> spoofing that isn't in a debugging or troubleshooting context and
> would be more comfortable if it were not possible at all... Anyone
> know of a program that relies on this spoofing functionality?
>
> If you look at socket(7) under SO_PEERCRED there is a way to get
> credentials at time of connect() for an AF_UNIX SOCK_STREAM, or at
> time of socketpair() for a SOCK_DGRAM. I would like to think these
> credentials are reliable, but will probably require some extra daemon
> to proxy a dgram syslog socket.

Thanks for the comments Michael! The usecase we are considering involves 
non root monitor process be able to translate the process ID of other 
non-root processes under same user within nested PID namespaces. With 
SCM_CREDENTIALS method, we require open sockets and connections between 
the processes which require PID translation and also CAP_SYS_ADMIN which 
is higher than required privilege level for non-root monitor process. 
The current patch solves this problem by enabling to open the related 
procfs fd when required during PID translation. I believe almost 
everyone agreed on this V6 patch but not sure why it is in limbo still.

Thanks,
Nagarathnam.