linux-kernel - Re: [PATCH 2/6] ima: Return INTEGRITY_FAIL if digital signature can't be verified

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Message-ID: <20130304162033.GB15199@redhat.com>
Date:	Mon, 4 Mar 2013 11:20:33 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmitry.kasatkin@...el.com
Subject: Re: [PATCH 2/6] ima: Return INTEGRITY_FAIL if digital signature
 can't be verified

On Mon, Mar 04, 2013 at 08:48:36AM -0500, Mimi Zohar wrote:
> On Thu, 2013-02-14 at 14:55 -0500, Vivek Goyal wrote:
> > Digital signature verification happens using integrity_digsig_verify().
> > Curently we set integrity to FAIL for all error codes except -EOPNOTSUPP.
> > This sounds out of line.
> > 
> > - If appropriate kernel code is not compiled in to verify signature of
> >   a file, then prractically it is a failed signature.
> > 
> > - For so many other possible errors we are setting the status to fail.
> >   For example, -EINVAL, -ENOKEY, -ENOMEM, -EINVAL, -ENOTSUPP etc, it
> >   beats me that why -EOPNOTSUPP is special.
> > 
> > This patch should make the semantics more consistent. That is, if digital
> > signature is present in security.ima, then any error happened during
> > signature processing leads to status INTEGRITY_FAIL.
> > 
> > AFAICS, it should not have any user visible effect on existing
> > application. In some cases we will start returning INTEGRITY_FAIL
> > instead of INTEGRITY_UNKNOWN. And process_measurement() will deny access
> > to file both in case of INTEGRITY_UNKNOWN and INTEGRITY_FAIL.
> > 
> > Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> 
> A number of patches in this patchset more finely differentiate return
> codes, which is good.  I agree with you totally that there is no good
> reason for -EOPNOTSUPP to be handled differently.  Unfortunately, the
> initramfs is CPIO, which doesn't support xattrs.  With the proposed
> change and 'ima_appraise_tcb' flag enabled, we wouldn't be able to boot.
> I really dislike hard coding policy in the kernel.

Hi Mimi,

If there are no xattr, then we will not even hit this code. We will
bail out early in vfs_getxattr_alloc().

I thought that one of the DON_APPRAISE rules will kick in for initramfs
and files in initramfs will not be appraised and boot will continue.

{.action = DONT_APPRAISE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
{.action = DONT_APPRAISE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC},

Is that not the case here?

Thanks
Vivek
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