From: Mimi Zohar <zohar@linux.ibm.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
Amir Goldstein <amir73il@gmail.com>
Cc: iforster@suse.de, Goldwyn Rodrigues <rgoldwyn@suse.com>,
linux-integrity@vger.kernel.org,
Miklos Szeredi <miklos@szeredi.hu>,
overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: EVM: Permission denied with overlayfs
Date: Thu, 20 Dec 2018 09:55:16 -0500 [thread overview]
Message-ID: <1545317716.4077.33.camel@linux.ibm.com> (raw)
In-Reply-To: <1545257296.2916.42.camel@HansenPartnership.com>
On Wed, 2018-12-19 at 14:08 -0800, James Bottomley wrote:
> > For portable signatures, to bind the file metadata with the file
> > data, we've replaced the inode number and generation, with the
> > "security.ima" xattr. Do we want this requirement/limitation for
> > overlays?
>
> Well, that's my question, yes. I think there's a reasonable case for
> it, but I was wondering what value the inode number and generation
> brings. Is there some reason to bind the EVM signature to a more
> mutable file container (which is what inum/generation provide) rather
> than a hard hash of file content (which is what the ima xattr
> provides)?
As only files in the IMA policy are labeled with security.ima, to
protect other files and directories, requires including the inode
number, generation and the UUID.
> > The existing EVM portable signature is an asymmetric algorithm based
> > signature. Would we define a "portable" HMAC?
>
> Well, a signature is just an encryption of a hash. Whether you do HMAC
> with symmetric key or RSA/EC with an asymmetric one is more an
> operational question. HMAC is certainly much faster but EVM only has a
> single hmac key which is problematic for the containers. Without a use
> case I can't really say. Instinct tells me asymmetric is more suitable
> to the container use case, but that's really just a guess.
One of the differences between the EVM portable signature type and the
original signature type is that the portable signatures aren't
replaced with an HMAC. They're considered portable & immutable.
Adding kernel support for signing mutable files using an asymmetric
key is going to blur the lines between mutable/immutable files.
Mimi
next prev parent reply other threads:[~2018-12-20 14:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-18 19:49 EVM: Permission denied with overlayfs Ignaz Forster
2018-12-18 23:00 ` Mimi Zohar
2018-12-19 15:39 ` Mimi Zohar
2018-12-19 16:38 ` Amir Goldstein
2018-12-19 18:34 ` Mimi Zohar
2018-12-19 20:39 ` Amir Goldstein
2018-12-20 3:42 ` Goldwyn Rodrigues
2018-12-20 7:15 ` Amir Goldstein
2018-12-19 16:56 ` James Bottomley
2018-12-19 18:15 ` Mimi Zohar
2018-12-19 19:34 ` James Bottomley
2018-12-19 20:12 ` Amir Goldstein
2018-12-19 21:02 ` Mimi Zohar
2018-12-19 22:08 ` James Bottomley
2018-12-20 14:55 ` Mimi Zohar [this message]
2018-12-20 19:24 ` James Bottomley
2018-12-19 22:11 ` James Bottomley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1545317716.4077.33.camel@linux.ibm.com \
--to=zohar@linux.ibm.com \
--cc=James.Bottomley@HansenPartnership.com \
--cc=amir73il@gmail.com \
--cc=iforster@suse.de \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-unionfs@vger.kernel.org \
--cc=miklos@szeredi.hu \
--cc=rgoldwyn@suse.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).