Re: [libvirt] [libvirt-users] virRandomBits - not very random
Reviving an ancient thread: On 11/04/2014 02:18 AM, Daniel P. Berrange wrote:
On Mon, Nov 03, 2014 at 11:09:12AM -0500, Brian Rak wrote:
I just ran into an issue where I had about 30 guests get duplicate mac addresses assigned. These were scattered across 30 different machines.
Some debugging revealed that:
1) All the host machines were restarted within a couple seconds of each other 2) All the host machines had fairly similar libvirtd pids (within ~100 PIDs of each other) 3) Libvirt seeds the RNG using 'time(NULL) ^ getpid()'
This perfectly explains why I saw so many duplicate mac addresses.
Why is the RNG seed such a predictable value? Surely there has to be a better source of a random seed then the timestamp and the pid?
The PID seems to me to be a very bad source of any randomness. I just ran a test across 60 of our hosts. 43 of them shared their PID with at least one other machine.
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
Did anyone ever open a BZ to track this? As far as I can tell, we still have a very predictable (meaning bad) seeding algorithm that permits large clusters to create collisions when their random number sequences sync up. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
On 5/25/2018 8:58 AM, Eric Blake wrote:
Reviving an ancient thread:
On 11/04/2014 02:18 AM, Daniel P. Berrange wrote:
On Mon, Nov 03, 2014 at 11:09:12AM -0500, Brian Rak wrote:
I just ran into an issue where I had about 30 guests get duplicate mac addresses assigned. These were scattered across 30 different machines.
Some debugging revealed that:
1) All the host machines were restarted within a couple seconds of each other 2) All the host machines had fairly similar libvirtd pids (within ~100 PIDs of each other) 3) Libvirt seeds the RNG using 'time(NULL) ^ getpid()'
This perfectly explains why I saw so many duplicate mac addresses.
Why is the RNG seed such a predictable value? Surely there has to be a better source of a random seed then the timestamp and the pid?
The PID seems to me to be a very bad source of any randomness. I just ran a test across 60 of our hosts. 43 of them shared their PID with at least one other machine.
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
Did anyone ever open a BZ to track this? As far as I can tell, we still have a very predictable (meaning bad) seeding algorithm that permits large clusters to create collisions when their random number sequences sync up.
I never did. We just switched to maintaining the mac ourselves, and not letting libvirt generate it.
On 05/25/2018 02:58 PM, Eric Blake wrote:
Reviving an ancient thread:
On 11/04/2014 02:18 AM, Daniel P. Berrange wrote:
On Mon, Nov 03, 2014 at 11:09:12AM -0500, Brian Rak wrote:
I just ran into an issue where I had about 30 guests get duplicate mac addresses assigned. These were scattered across 30 different machines.
Some debugging revealed that:
1) All the host machines were restarted within a couple seconds of each other 2) All the host machines had fairly similar libvirtd pids (within ~100 PIDs of each other) 3) Libvirt seeds the RNG using 'time(NULL) ^ getpid()'
This perfectly explains why I saw so many duplicate mac addresses.
Why is the RNG seed such a predictable value? Surely there has to be a better source of a random seed then the timestamp and the pid?
The PID seems to me to be a very bad source of any randomness. I just ran a test across 60 of our hosts. 43 of them shared their PID with at least one other machine.
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now. Michal
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up: https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed. If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits). So at this point, it's just a matter of someone writing the patches. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd(). 1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html Michal
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
We should probably seed it with data from /dev/urandom, and/or the new Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment: https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html and since IIUC that's not an issue any more.... John now if I could only figure out why my mail client seems to be dropping any patches with "crypto" in the subject line (I'm missing patches 2-4 and 10 from the series referenced above)...
On Tue, May 29, 2018 at 10:06:25AM -0400, John Ferlan wrote:
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
> We should probably seed it with data from /dev/urandom, and/or the new > Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment:
https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html
and since IIUC that's not an issue any more....
Oh, cool to know. Michal also found the patch [1] where Dan switched the gnutls from being mandatory to making it optional and there is no explanation for that change in the commit message: [1] f587c27768ee13f5bed6a9262106307b7a124403
John
now if I could only figure out why my mail client seems to be dropping any patches with "crypto" in the subject line (I'm missing patches 2-4 and 10 from the series referenced above)...
Maybe you have some weird server-side filter for it?
On Wed, May 30, 2018 at 10:21:54PM +0200, Martin Kletzander wrote:
On Tue, May 29, 2018 at 10:06:25AM -0400, John Ferlan wrote:
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
> > We should probably seed it with data from /dev/urandom, and/or the new > > Linux getrandom() syscall (or BSD equivalent).
I'm not quite sure that right after reboot there's going to be enough entropy. Every service that's starting wants some random bits. But it's probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment:
https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html
and since IIUC that's not an issue any more....
Oh, cool to know. Michal also found the patch [1] where Dan switched the gnutls from being mandatory to making it optional and there is no explanation for that change in the commit message:
[1] f587c27768ee13f5bed6a9262106307b7a124403
Not all usage scenarios in libvirt have required GNUTLS - only the remote driver, when using stateful virt drivers. If you're just biulding libvirt for usage with ESX/HyperV/etc, there's no reason you'd want GNUTLS historically. Also note when building the setuid libvirt pieces we must never use GNUTLS because its library constructors do very bad things leading to CVEs. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Fri, Jun 01, 2018 at 11:17:44AM +0100, Daniel P. Berrangé wrote:
On Wed, May 30, 2018 at 10:21:54PM +0200, Martin Kletzander wrote:
On Tue, May 29, 2018 at 10:06:25AM -0400, John Ferlan wrote:
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote:
On 05/25/2018 09:17 AM, Michal Privoznik wrote:
> > > We should probably seed it with data from /dev/urandom, and/or the new > > > Linux getrandom() syscall (or BSD equivalent). > > I'm not quite sure that right after reboot there's going to be enough > entropy. Every service that's starting wants some random bits. But it's > probably better than what we have now.
Here's where we left things last time it came up:
https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html
If gnutls has an interface that will give us random bits (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of our random bits (and forget about a seed), except when we are mocking things in our testsuite, and need a deterministic PRNG from a deterministic seed.
If not (including if we are not linked with gnutls), then we should prefer the new Linux syscall but fall back to /dev/urandom for JUST enough bits for a seed; once we're seeded, stick with using our existing PRNG for all future bits (after all, we aren't trying to generate cryptographically secure keys using virRandomBits - and the places where we DO need crypto-strong randomness such as setting up TLS migration is where we are relying on gnutls to provide it rather than virRandomBits).
So at this point, it's just a matter of someone writing the patches.
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment:
https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html
and since IIUC that's not an issue any more....
Oh, cool to know. Michal also found the patch [1] where Dan switched the gnutls from being mandatory to making it optional and there is no explanation for that change in the commit message:
[1] f587c27768ee13f5bed6a9262106307b7a124403
Not all usage scenarios in libvirt have required GNUTLS - only the remote driver, when using stateful virt drivers. If you're just biulding libvirt for usage with ESX/HyperV/etc, there's no reason you'd want GNUTLS historically.
Also note when building the setuid libvirt pieces we must never use GNUTLS because its library constructors do very bad things leading to CVEs.
Good to know, thanks for the info. I'll need to read up on the gnutls constructors (is it just gnutls or some other libs as well?) even though I remember researching something related to it some time ago. However that doesn't mean it has to be optional. Do you think there are people who would be bothered by the requirement of gnutls? I'm sure most of them have gnutls anyway. Some of them even need to have, for example if you have a look at virCryptoHashBuf() its stub returns -1 and it is used in ESX. If you compile without GNUTLS, all the functions that require it will just fail and it's not something that is used rarely. We can we make it required only if you are building with qemu or remote or esx or basically something that requires it. Encryption of RAW volumes for example. Or lock driver. But I don't think there are some who run the builds themselves and doesn't want gnutls on their system. I can't think of a reason for having it and not linking libvirt with it.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
On Fri, Jun 01, 2018 at 02:01:03PM +0200, Martin Kletzander wrote:
On Fri, Jun 01, 2018 at 11:17:44AM +0100, Daniel P. Berrangé wrote:
On Wed, May 30, 2018 at 10:21:54PM +0200, Martin Kletzander wrote:
On Tue, May 29, 2018 at 10:06:25AM -0400, John Ferlan wrote:
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote:
On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote: > On 05/25/2018 09:17 AM, Michal Privoznik wrote: > > > > > We should probably seed it with data from /dev/urandom, and/or the new > > > > Linux getrandom() syscall (or BSD equivalent). > > > > I'm not quite sure that right after reboot there's going to be enough > > entropy. Every service that's starting wants some random bits. But it's > > probably better than what we have now. > > Here's where we left things last time it came up: > > https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html > > If gnutls has an interface that will give us random bits > (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of > our random bits (and forget about a seed), except when we are mocking > things in our testsuite, and need a deterministic PRNG from a > deterministic seed. > > If not (including if we are not linked with gnutls), then we should > prefer the new Linux syscall but fall back to /dev/urandom for JUST > enough bits for a seed; once we're seeded, stick with using our existing > PRNG for all future bits (after all, we aren't trying to generate > cryptographically secure keys using virRandomBits - and the places where > we DO need crypto-strong randomness such as setting up TLS migration is > where we are relying on gnutls to provide it rather than virRandomBits). > > So at this point, it's just a matter of someone writing the patches. >
Actually, do we need to have a fallback at all? Can't we just drop all the gross parts of the code the conditionally compile based on GNUTLS support? Why don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment:
https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html
and since IIUC that's not an issue any more....
Oh, cool to know. Michal also found the patch [1] where Dan switched the gnutls from being mandatory to making it optional and there is no explanation for that change in the commit message:
[1] f587c27768ee13f5bed6a9262106307b7a124403
Not all usage scenarios in libvirt have required GNUTLS - only the remote driver, when using stateful virt drivers. If you're just biulding libvirt for usage with ESX/HyperV/etc, there's no reason you'd want GNUTLS historically.
Also note when building the setuid libvirt pieces we must never use GNUTLS because its library constructors do very bad things leading to CVEs.
Good to know, thanks for the info. I'll need to read up on the gnutls constructors (is it just gnutls or some other libs as well?) even though I remember researching something related to it some time ago. However that doesn't mean it has to be optional.
Do you think there are people who would be bothered by the requirement of gnutls? I'm sure most of them have gnutls anyway. Some of them even need to have, for example if you have a look at virCryptoHashBuf() its stub returns -1 and it is used in ESX. If you compile without GNUTLS, all the functions that require it will just fail and it's not something that is used rarely.
We can we make it required only if you are building with qemu or remote or esx or basically something that requires it. Encryption of RAW volumes for example. Or lock driver. But I don't think there are some who run the builds themselves and doesn't want gnutls on their system. I can't think of a reason for having it and not linking libvirt with it.
I should clarify - I've no objection to making GNUTLS mandatory at configure time - just that we need to continue to have WITH_GNUTLS conditionals in some parts of the code in order to support the setuid build without GNUTLS. So we might be able to remove some of the WITH_GNUTLS bits, but not all of them. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Fri, Jun 01, 2018 at 01:25:26PM +0100, Daniel P. Berrangé wrote:
On Fri, Jun 01, 2018 at 02:01:03PM +0200, Martin Kletzander wrote:
On Fri, Jun 01, 2018 at 11:17:44AM +0100, Daniel P. Berrangé wrote:
On Wed, May 30, 2018 at 10:21:54PM +0200, Martin Kletzander wrote:
On Tue, May 29, 2018 at 10:06:25AM -0400, John Ferlan wrote:
On 05/29/2018 09:44 AM, Michal Privoznik wrote:
On 05/29/2018 03:38 PM, Martin Kletzander wrote: > On Fri, May 25, 2018 at 09:37:44AM -0500, Eric Blake wrote: > > On 05/25/2018 09:17 AM, Michal Privoznik wrote: > > > > > > > We should probably seed it with data from /dev/urandom, and/or the new > > > > > Linux getrandom() syscall (or BSD equivalent). > > > > > > I'm not quite sure that right after reboot there's going to be enough > > > entropy. Every service that's starting wants some random bits. But it's > > > probably better than what we have now. > > > > Here's where we left things last time it came up: > > > > https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html > > > > If gnutls has an interface that will give us random bits > > (gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of > > our random bits (and forget about a seed), except when we are mocking > > things in our testsuite, and need a deterministic PRNG from a > > deterministic seed. > > > > If not (including if we are not linked with gnutls), then we should > > prefer the new Linux syscall but fall back to /dev/urandom for JUST > > enough bits for a seed; once we're seeded, stick with using our existing > > PRNG for all future bits (after all, we aren't trying to generate > > cryptographically secure keys using virRandomBits - and the places where > > we DO need crypto-strong randomness such as setting up TLS migration is > > where we are relying on gnutls to provide it rather than virRandomBits). > > > > So at this point, it's just a matter of someone writing the patches. > > > > Actually, do we need to have a fallback at all? Can't we just drop all the > gross parts of the code the conditionally compile based on GNUTLS > support? Why > don't we have gnutls required?
That's exactly what I'm suggesting in my patches [1]. gnutls is widely available (including Linux, Windows, *BSD, Mac Os X). However, before doing that we need to fix virRandomBits() to actually call gnutls_rnd().
1: https://www.redhat.com/archives/libvir-list/2018-May/msg02077.html
I have this faint recollection of one of the CI platform builds failing because something in the gnutls* family didn't exist there when I was making the changes to add the domain master secret code.... After a bit of digging, it seems it was a perhaps a CENTOS6 environment:
https://www.redhat.com/archives/libvir-list/2016-April/msg00287.html
and since IIUC that's not an issue any more....
Oh, cool to know. Michal also found the patch [1] where Dan switched the gnutls from being mandatory to making it optional and there is no explanation for that change in the commit message:
[1] f587c27768ee13f5bed6a9262106307b7a124403
Not all usage scenarios in libvirt have required GNUTLS - only the remote driver, when using stateful virt drivers. If you're just biulding libvirt for usage with ESX/HyperV/etc, there's no reason you'd want GNUTLS historically.
Also note when building the setuid libvirt pieces we must never use GNUTLS because its library constructors do very bad things leading to CVEs.
Good to know, thanks for the info. I'll need to read up on the gnutls constructors (is it just gnutls or some other libs as well?) even though I remember researching something related to it some time ago. However that doesn't mean it has to be optional.
Do you think there are people who would be bothered by the requirement of gnutls? I'm sure most of them have gnutls anyway. Some of them even need to have, for example if you have a look at virCryptoHashBuf() its stub returns -1 and it is used in ESX. If you compile without GNUTLS, all the functions that require it will just fail and it's not something that is used rarely.
We can we make it required only if you are building with qemu or remote or esx or basically something that requires it. Encryption of RAW volumes for example. Or lock driver. But I don't think there are some who run the builds themselves and doesn't want gnutls on their system. I can't think of a reason for having it and not linking libvirt with it.
I should clarify - I've no objection to making GNUTLS mandatory at configure time - just that we need to continue to have WITH_GNUTLS conditionals in some parts of the code in order to support the setuid build without GNUTLS. So we might be able to remove some of the WITH_GNUTLS bits, but not all of them.
Oh, OK. Great.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
participants (6)
-
Brian Rak -
Daniel P. Berrangé -
Eric Blake -
John Ferlan -
Martin Kletzander -
Michal Privoznik