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Thu, 6 Jun 2019 18:56:09 +0000 Received: from c-73-223-4-185.hsd1.ca.comcast.net (EHLO [192.168.0.103]) ([73.223.4.185]) by smtp418.mail.gq1.yahoo.com (Oath Hermes SMTP Server) with ESMTPA ID 75f9577105f271864dda01fe6e35d536; Thu, 06 Jun 2019 18:56:07 +0000 (UTC) Subject: Re: [RFC][PATCH 00/10] Mount, FS, Block and Keyrings notifications [ver #3] To: Stephen Smalley , David Howells Cc: viro@zeniv.linux.org.uk, Greg Kroah-Hartman , linux-usb@vger.kernel.org, raven@themaw.net, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-block@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Paul Moore , casey@schaufler-ca.com References: <155981411940.17513.7137844619951358374.stgit@warthog.procyon.org.uk> <3813.1559827003@warthog.procyon.org.uk> <8382af23-548c-f162-0e82-11e308049735@tycho.nsa.gov> <0eb007c5-b4a0-9384-d915-37b0e5a158bf@schaufler-ca.com> From: Casey Schaufler Openpgp: preference=signencrypt Autocrypt: addr=casey@schaufler-ca.com; 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WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/6/2019 10:16 AM, Stephen Smalley wrote: > On 6/6/19 12:43 PM, Casey Schaufler wrote: >> ... >> I don't agree. That is, I don't believe it is sufficient. >> There is no guarantee that being able to set a watch on an >> object implies that every process that can trigger the event >> can send it to you. >> >> =C2=A0=C2=A0=C2=A0=C2=A0Watcher has Smack label W >> =C2=A0=C2=A0=C2=A0=C2=A0Triggerer has Smack label T >> =C2=A0=C2=A0=C2=A0=C2=A0Watched object has Smack label O >> >> =C2=A0=C2=A0=C2=A0=C2=A0Relevant Smack rules are >> >> =C2=A0=C2=A0=C2=A0=C2=A0W O rw >> =C2=A0=C2=A0=C2=A0=C2=A0T O rw >> >> The watcher will be able to set the watch, >> the triggerer will be able to trigger the event, >> but there is nothing that would allow the watcher >> to receive the event. This is not a case of watcher >> reading the watched object, as the event is delivered >> without any action by watcher. > > You are allowing arbitrary information flow between T and W above.=C2=A0= Who cares about notifications? I do. If Watched object is /dev/null no data flow is possible. There are many objects on a modern Linux system for which this is true. Even if it's "just a file" the existence of one path for data to flow does not justify ignoring the rules for other data paths. > > How is it different from W and T mapping the same file as a shared mapp= ing and communicating by reading and writing the shared memory?=C2=A0 You= aren't performing a permission check directly between W and T there. In this case there is one object O, two subjects, W and T and two accesse= s. W open O T open O They fiddle about with the data in O. In the event case, there are two objects, O and W, two subjects W and T, = and three accesses. W watch O T trigger O T write-event W You can't wave away the flow of data. Different objects are involved. An analogy is that two processes with different UIDs can open a file, but still can't signal each other. Different mechanisms have different policies. I'm not saying that's good, but it's the context we're in.