linux-kernel - Re: [PATCH] capabilities: Introduce CAP

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Date:   Wed, 27 May 2020 09:46:00 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Adrian Reber <areber@...hat.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        Michał Cłapiński <mclapinski@...gle.com>,
        Kamil Yurtsever <kyurtsever@...gle.com>,
        Dirk Petersen <dipeit@...il.com>,
        Christine Flood <chf@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Arnd Bergmann <arnd@...db.de>,
        Aaron Goidel <acgoide@...ho.nsa.gov>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        Eric Paris <eparis@...isplace.org>,
        Jann Horn <jannh@...gle.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] capabilities: Introduce CAP_RESTORE

On 5/27/2020 9:37 AM, Nicolas Viennot wrote:
>>> If I understand part of CRIU correctly, then we only need read-access 
>>> for the current user. I am sure Andrei, Pavel or Cyrill will correct 
>>> me if I am wrong concerning map_files.
>> If I do "ls -l /proc/self/map_files" I get the link name and link content.
>> While I can't open /proc/self/map_files/7fbde0c3200-7fbde0c3300 I can read that it points to /usr/lib64/ld-2.30.so, which is something I can open and read. Sure, it's an extra step, but it's no big deal. It does raise the question of what value comes from disallowing open via the symlink.
> Reading the symlink doesn't work in two cases:
> 1) The file has been deleted

In which case you won't be able to read it directly from
the symlink, either.

> 2) The file is a memfd file

Ditto? Or is there some other problem?