linux-kernel - Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial ram disk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190515002556.GA88615@rani.riverdale.lan>
Date:   Tue, 14 May 2019 20:25:57 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Rob Landley <rob@...dley.net>,
        Arvind Sankar <niveditas98@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        initramfs@...r.kernel.org
Subject: Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial
 ram disk

On Tue, May 14, 2019 at 07:20:15PM +0200, Roberto Sassu wrote:
> On 5/14/2019 6:58 PM, Greg KH wrote:
> > On Tue, May 14, 2019 at 06:33:29PM +0200, Roberto Sassu wrote:
> >> Right, the measurement/signature verification of the kernel image is
> >> sufficient.
> >>
> >> Now, assuming that we defer the IMA initialization until /init in the
> >> embedded initramfs has been executed, the problem is how to handle
> >> processes launched with the user mode helper or files directly read by
> >> the kernel (if it can happen before /init is executed). If IMA is not
> >> yet enabled, these operations will be performed without measurement and
> >> signature verification.
> > 
> > If you really care about this, don't launch any user mode helper
> > programs (hint, you have the kernel option to control this and funnel
> > everything into one, or no, binaries).  And don't allow the kernel to
> > read any files either, again, you have control over this.
> > 
> > Or start IMA earlier if you need/want/care about this.
> 
> Yes, this is how it works now. It couldn't start earlier than
> late_initcall, as it has to wait until the TPM driver is initialized.
> 
> Anyway, it is enabled at the time /init is executed. And this would be
> an issue because launching /init and reading xattrs from /.xattr-list
> would be denied (the signature is missing).
> 
> And /.xattr-list won't have a signature, if initramfs is generated
> locally.
> 
> Roberto
> 
> -- 
> HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
> Managing Director: Bo PENG, Jian LI, Yanli SHI

The uevent and firmware loader user mode helpers are both obsolete I
believe, so those shouldn't be an issue.

There is still the internal firmware loader (CONFIG_FW_LOADER). If this
is built-in, there's probably no way to 100% stop it racing with /init if we
depend on an embedded /init and a malicious external initramfs image
contains /lib/firmware, but it can be built as an external module, in
which case there should be no danger until the boot process actually loads it.