From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 5077091A for ; Mon, 1 Aug 2016 23:13:53 +0000 (UTC) Received: from mail-ua0-f171.google.com (mail-ua0-f171.google.com [209.85.217.171]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 6D1B310A for ; Mon, 1 Aug 2016 23:13:52 +0000 (UTC) Received: by mail-ua0-f171.google.com with SMTP id j59so117048586uaj.3 for ; Mon, 01 Aug 2016 16:13:52 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160801230435.GF4541@io.lakedaemon.net> References: <1469934481.23563.274.camel@linux.vnet.ibm.com> <1469979098.23563.300.camel@linux.vnet.ibm.com> <1469986138.23563.312.camel@linux.vnet.ibm.com> <20160801172920.GU3296@wotan.suse.de> <1470090069.23563.475.camel@linux.vnet.ibm.com> <20160801230435.GF4541@io.lakedaemon.net> From: Andy Lutomirski Date: Mon, 1 Aug 2016 16:13:50 -0700 Message-ID: To: Jason Cooper Content-Type: multipart/alternative; boundary=94eb2c122f02da597805390ac0bc Cc: James Bottomley , Mark Brown , "ksummit-discuss@lists.linuxfoundation.org" Subject: Re: [Ksummit-discuss] Last minute nominations: mcgrof and toshi List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --94eb2c122f02da597805390ac0bc Content-Type: text/plain; charset=UTF-8 On Aug 1, 2016 4:04 PM, "Jason Cooper" wrote: > > On Mon, Aug 01, 2016 at 03:36:51PM -0700, Andy Lutomirski wrote: > > On Mon, Aug 1, 2016 at 3:21 PM, Mimi Zohar wrote: > > > On Mo, 2016-08-01 at 10:59 -0700, Andy Lutomirski wrote: > > > > > >> Mimi, I'm curious: I don't fully understand what is covered by IMA > > >> policy. How does the IMA kernel_read_file stuff deal with symlinks? > > >> For example, if I symlink /lib/firmware/iwlwifi-8265-21.ucode to > > >> /home/badguy/iwlwifi-8265-21.ucode, what happens? What if I symlink > > >> /lib/firmware/iwlwifi-8265-21.ucode to /home/badguy/something_else? > > >> Or even /lib/modules/kernel/foo/bar.ko to /home/badguy/evil.ko? The > > >> interesting case is where the "badguy" user is duly authorized to > > >> write to /home/badguy and holds whatever keys may be needed. > > > > > > Lets step back a second. In order for a key to be added to the IMA > > > keyring, the key must be signed by a key on the builtin keyring. The > > > key on the builtin keyring can be compiled into the kernel image or > > > added post build using Mehmet Kayaalp's patches. > > > > > > True, any key on the IMA keyring could be used to verify file signatures > > > (in IMA terminology appraise the file's integrity). The enumeration is > > > a first step to making sure that only properly signed code is read by > > > the kernel. The next step requires finer grain key management. In > > > general, pathname based policies are not a good idea. Whatever method > > > is defined, it should not be limited to just firmware or files read by > > > the kernel, but to all files. > > > > > > > Unless I'm mistaken (which is quite possible), IMA is primarily > > intended to appraise the content of POSIX filesystems. So, if IMA is > > in use, then doing: > > > > $ cat /foo/bar > > > > should only succeed if /foo/bar is signed according to loaded policy. > > It's the system administrator's decision what filesystem is actually > > mounted at /foo, and root can presumably mess around with application > > expectations by, say, bind-mounting something over /foo. > > > > Modules and firmware are special: even root should not be able to > > avoid the full signature policy. This means that, for example: > > > > # mount --bind /evil /lib/firmware > > > > should not result in violating policy. So the pathname should not be > > used as such. However, firmware is a bit special in that the driver > > chooses the pathname to request, and it really does uniquely identify > > the intended firmware. So, when a driver asks for: > > > > "iwlwifi-whatever.ucode" > > > > and the driver core tries to read "/lib/firmware/iwlwifi-whatever.ucode" > > > > it's entirely possible that we'll follow a symlink and end up > > elsewhere (Fedora, for example, does exactly this), but the file > > that's loaded should be appraised (or verified using a non-IMA means, > > etc.) to verify that whatever blob gets found is actually signed by > > the holder of an authorized key for the purpose of being used as > > "iwlwifi-whatever.ucode". > > Assuming Andy's lightweight signature scheme, it would probably be best > to do a lookup based on the sha256 hash of the file. Then pathnames > don't matter, and bad files don't even get to the signature checking > code. > I'm not sure I understand what you mean. What table would we look the hash up in? What are we finding in that table? --94eb2c122f02da597805390ac0bc Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

On Aug 1, 2016 4:04 PM, "Jason Cooper" <jason@lakedaemon.net> wrote:
>
> On Mon, Aug 01, 2016 at 03:36:51PM -0700, Andy Lutomirski wrote:
> > On Mon, Aug 1, 2016 at 3:21 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> > > On Mo, 2016-08-01 at 10:59 -0700, Andy Lutomirski wrote:
> > >
> > >> Mimi, I'm curious: I don't fully understand what= is covered by IMA
> > >> policy.=C2=A0 How does the IMA kernel_read_file stuff de= al with symlinks?
> > >> For example, if I symlink /lib/firmware/iwlwifi-8265-21.= ucode to
> > >> /home/badguy/iwlwifi-8265-21.ucode, what happens?=C2=A0 = What if I symlink
> > >> /lib/firmware/iwlwifi-8265-21.ucode to /home/badguy/some= thing_else?
> > >> Or even /lib/modules/kernel/foo/bar.ko to /home/badguy/e= vil.ko?=C2=A0 The
> > >> interesting case is where the "badguy" user is= duly authorized to
> > >> write to /home/badguy and holds whatever keys may be nee= ded.
> > >
> > > Lets step back a second.=C2=A0 In order for a key to be adde= d to the IMA
> > > keyring, the key must be signed by a key on the builtin keyr= ing.=C2=A0 The
> > > key on the builtin keyring can be compiled into the kernel i= mage or
> > > added post build using Mehmet Kayaalp's patches.
> > >
> > > True, any key on the IMA keyring could be used to verify fil= e signatures
> > > (in IMA terminology appraise the file's integrity).=C2= =A0 The enumeration is
> > > a first step to making sure that only properly signed code i= s read by
> > > the kernel.=C2=A0 The next step requires finer grain key man= agement.=C2=A0 In
> > > general, pathname based policies are not a good idea.=C2=A0 = Whatever method
> > > is defined, it should not be limited to just firmware or fil= es read by
> > > the kernel, but to all files.
> > >
> >
> > Unless I'm mistaken (which is quite possible), IMA is primari= ly
> > intended to appraise the content of POSIX filesystems.=C2=A0 So, = if IMA is
> > in use, then doing:
> >
> > $ cat /foo/bar
> >
> > should only succeed if /foo/bar is signed according to loaded pol= icy.
> > It's the system administrator's decision what filesystem = is actually
> > mounted at /foo, and root can presumably mess around with applica= tion
> > expectations by, say, bind-mounting something over /foo.
> >
> > Modules and firmware are special: even root should not be able to=
> > avoid the full signature policy.=C2=A0 This means that, for examp= le:
> >
> > # mount --bind /evil /lib/firmware
> >
> > should not result in violating policy.=C2=A0 So the pathname shou= ld not be
> > used as such.=C2=A0 However, firmware is a bit special in that th= e driver
> > chooses the pathname to request, and it really does uniquely iden= tify
> > the intended firmware.=C2=A0 So, when a driver asks for:
> >
> > "iwlwifi-whatever.ucode"
> >
> > and the driver core tries to read "/lib/firmware/iwlwifi-wha= tever.ucode"
> >
> > it's entirely possible that we'll follow a symlink and en= d up
> > elsewhere (Fedora, for example, does exactly this), but the file<= br> > > that's loaded should be appraised (or verified using a non-IM= A means,
> > etc.) to verify that whatever blob gets found is actually signed = by
> > the holder of an authorized key for the purpose of being used as<= br> > > "iwlwifi-whatever.ucode".
>
> Assuming Andy's lightweight signature scheme, it would probably be= best
> to do a lookup based on the sha256 hash of the file.=C2=A0 Then pathna= mes
> don't matter, and bad files don't even get to the signature ch= ecking
> code.
>

I'm not sure I understand what you mean.=C2=A0 What tabl= e would we look the hash up in?=C2=A0 What are we finding in that table?

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