From: Casey Schaufler <firstname.lastname@example.org> To: David Howells <email@example.com>, Andy Lutomirski <firstname.lastname@example.org> Cc: Al Viro <email@example.com>, firstname.lastname@example.org, Linux FS Devel <email@example.com>, Linux API <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, LSM List <email@example.com>, LKML <firstname.lastname@example.org>, email@example.com Subject: Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] Date: Tue, 4 Jun 2019 14:11:45 -0700 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 6/4/2019 1:39 PM, David Howells wrote: > Andy Lutomirski <firstname.lastname@example.org> wrote: > >>> Here's a set of patches to add a general variable-length notification queue >>> concept and to add sources of events for: >> I asked before and didn't see a response, so I'll ask again. Why are you >> paying any attention at all to the creds that generate an event? > Casey responded to you. It's one of his requirements. Process A takes an action. As a result of that action, an event is written to Process B's event buffer. This isn't a covert channel, it's a direct access, just like sending a signal. Process A is the subject and the event buffer, which is part of Process B, is the object. > I'm not sure of the need, and I particularly don't like trying to make > indirect destruction events (mount destruction keyed on fput, for instance) > carry the creds of the triggerer. Indeed, the trigger can come from all sorts > of places - including af_unix queue destruction, someone poking around in > procfs, a variety of processes fputting simultaneously. Only one of them can > win, and the LSM needs to handle *all* the possibilities. Yes, it's a hairy problem. It was a significant factor in the demise of kdbus. > However, the LSMs (or at least SELinux) ignore f_cred and use current_cred() > when checking permissions. See selinux_revalidate_file_permission() for > example - it uses current_cred() not file->f_cred to re-evaluate the perms, > and the fd might be shared between a number of processes with different creds. > >> This seems like the wrong approach. If an LSM wants to prevent covert >> communication from, say, mount actions, then it shouldn't allow the >> watch to be set up in the first place. > Yeah, I can agree to that. Casey? Back to your earlier point, you don't know where the event is coming from when you create the event watch. If you enforce a watch time, what are you going to check? Isn't this going to be considered too restrictive?
prev parent reply index Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-04 16:34 David Howells 2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells 2019-06-04 18:15 ` Andy Lutomirski 2019-06-04 16:35 ` [PATCH 2/8] General notification queue with user mmap()'able ring buffer " David Howells 2019-06-04 16:35 ` [PATCH 3/8] keys: Add a notification facility " David Howells 2019-06-04 16:35 ` [PATCH 4/8] vfs: Add a mount-notification " David Howells 2019-06-04 16:35 ` [PATCH 5/8] vfs: Add superblock notifications " David Howells 2019-06-04 16:36 ` [PATCH 6/8] fsinfo: Export superblock notification counter " David Howells 2019-06-04 16:36 ` [PATCH 7/8] block: Add block layer notifications " David Howells 2019-06-04 16:36 ` [PATCH 8/8] Add sample notification program " David Howells 2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski 2019-06-04 20:31 ` Casey Schaufler 2019-06-04 21:05 ` Andy Lutomirski 2019-06-04 22:03 ` Casey Schaufler 2019-06-05 8:41 ` David Howells 2019-06-05 14:50 ` Casey Schaufler 2019-06-05 16:04 ` Andy Lutomirski 2019-06-05 17:01 ` Casey Schaufler 2019-06-05 17:47 ` Andy Lutomirski 2019-06-05 18:12 ` Casey Schaufler 2019-06-05 18:25 ` Stephen Smalley 2019-06-05 19:28 ` Greg KH 2019-06-05 21:01 ` Stephen Smalley 2019-06-05 16:56 ` Rational model for UID based controls David Howells 2019-06-05 17:40 ` Casey Schaufler 2019-06-05 21:06 ` David Howells 2019-06-05 17:21 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells 2019-06-04 20:39 ` David Howells 2019-06-04 20:57 ` Andy Lutomirski [not found] ` <CAB9W1A0AgMYOwGx9c-TmAt=1O6Bjsr2P3Nhd=2+QV39dgw0CrA@mail.gmail.com> 2019-06-05 4:19 ` Andy Lutomirski 2019-06-05 13:47 ` Stephen Smalley 2019-06-04 21:11 ` Casey Schaufler [this message]
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