linux-kernel - Re: [RFC][PATCH 00/10] Mount, FS, Block and Keyrings notifications [ver #3]

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Date:   Thu, 6 Jun 2019 15:42:06 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     David Howells <dhowells@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>, raven@...maw.net,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-block@...r.kernel.org, keyrings@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>
Subject: Re: [RFC][PATCH 00/10] Mount, FS, Block and Keyrings notifications [ver #3]



> On Jun 6, 2019, at 3:38 PM, David Howells <dhowells@...hat.com> wrote:
> 
> Andy Lutomirski <luto@...capital.net> wrote:
> 
>> I mean: are there cases where some action generates a notification but does
>> not otherwise have an effect visible to the users who can receive the
>> notification. It looks like the answer is probably “no”, which is good.
> 
> mount_notify().  You can get a notification that someone altered the mount
> topology (eg. by mounting something).  A process receiving a notification
> could then use fsinfo(), say, to reread the mount topology tree, find out
> where the new mount is and wander over there to have a look - assuming they
> have the permissions for pathwalk to succeed.
> 
> 

They can call fsinfo() anyway, or just read /proc/self/mounts. As far as I’m concerned, if you have CAP_SYS_ADMIN over a mount namespace and LSM policy lets you mount things, the of course you can get information to basically anyone who can use that mount namespace.