Re: [libvirt] [PATCH v10 2/4] domain: Add optional 'tls' attribute for TCP chardev

On 10/20/2016 02:51 AM, Pavel Hrdina wrote: > On Wed, Oct 19, 2016 at 04:53:54PM -0400, John Ferlan wrote: >> Add an optional "tls='yes|no'" attribute for a TCP chardev. >> >> For QEMU, this will allow for disabling the host config setting of the >> 'chardev_tls' for a domain chardev channel by setting the value to "no" or >> to attempt to use a host TLS environment when setting the value to "yes" >> when the host config 'chardev_tls' setting is disabled, but a TLS environment >> is configured via either the host config 'chardev_tls_x509_cert_dir' or >> 'default_tls_x509_cert_dir' >> >> Alter qemuDomainSupportTLSChardevTCP to augment the decision points for >> choosing whether to try to use TLS. >> >> Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; >> --- >> docs/formatdomain.html.in | 28 ++++++++++++ >> docs/schemas/domaincommon.rng | 5 +++ >> src/conf/domain_conf.c | 22 +++++++++- >> src/conf/domain_conf.h | 1 + >> src/qemu/qemu_command.c | 2 +- >> src/qemu/qemu_domain.c | 20 +++++++-- >> src/qemu/qemu_domain.h | 3 +- >> src/qemu/qemu_hotplug.c | 4 +- >> ...uxml2argv-serial-tcp-tlsx509-chardev-notls.args | 30 +++++++++++++ >> ...muxml2argv-serial-tcp-tlsx509-chardev-notls.xml | 50 ++++++++++++++++++++++ >> tests/qemuxml2argvtest.c | 3 ++ >> ...xml2xmlout-serial-tcp-tlsx509-chardev-notls.xml | 1 + >> tests/qemuxml2xmltest.c | 1 + >> 13 files changed, 162 insertions(+), 8 deletions(-) >> create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev-notls.args >> create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev-notls.xml >> create mode 120000 tests/qemuxml2xmloutdata/qemuxml2xmlout-serial-tcp-tlsx509-chardev-notls.xml >> >> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in >> index 9051178..da6be67 100644 >> --- a/docs/formatdomain.html.in >> +++ b/docs/formatdomain.html.in >> @@ -6204,6 +6204,34 @@ qemu-kvm -net nic,model=? /dev/null >> &lt;/devices&gt; >> ...</pre> >> >> + <p> >> + <span class="since">Since 2.4.0,</span> the optional attribute >> + <code>tls</code> can be used to control whether a serial chardev >> + TCP communication channel would utilize a hypervisor configured >> + TLS X.509 certificate environment in order to encrypt the data >> + channel. For the QEMU hypervisor, usage of a TLS envronment can >> + be controlled on the host by the <code>chardev_tls</code> and >> + <code>chardev_tls_x509_cert_dir</code> or >> + <code>default_tls_x509_cert_dir</code> settings in the file >> + /etc/libvirt/qemu.conf. If <code>chardev_tls</code> is enabled, >> + then unless the <code>tls</code> attribute is set to "no", libvirt >> + will use the host configured TLS environment. >> + If <code>chardev_tls</code> is disabled, but the <code>tls</code> >> + attribute is set to "yes", then libvirt will attempt to use the >> + host TLS environment if either the <code>chardev_tls_x509_cert_dir</code> >> + or <code>default_tls_x509_cert_dir</code> TLS directory structure exists. >> + </p> > > Nice, this is a good description how to use the *tls* attribute. > BTW (regarding your followup reply): The 4 "consumers" of virDomainChrSourceDefParseXML (where this would be parsed) refer to this as a "serial chardev"

The 'virDomainChrDefParseXML' comments have a list of "<serial ..." XML types. The location of the above description is describing a <serial type="tcp"> definition.

The 'smartcard' discussion for a 'passthrough' device that would use this code says "Rather than having the hypervisor directly communicate with the host, it is possible to tunnel all requests through a secondary character device to a third-party provider (which may in turn be talking to a smartcard or using three certificate files). In this mode of operation, an additional attribute type is required, matching one of the supported serial device types, to describe the host side of the tunnel;..."

The 'rng' discussion for backend that would use this code says "This backend connects to a source using the EGD protocol. The source is specified as a character device. Refer to character device host interface for more information. ..."

Redevdir says "An additional attribute type is required, matching one of the supported serial device types, to describe the host side of the tunnel; type='tcp' or type='spicevmc' ..."

So the long and short of it is, IMO it's a serial chardev device. Semantically it could be claimed otherwise, but the parsing proves otherwise as does the existing documentation of "Host interface" character devices. I prefer to keep it described as is. It's only ever used, parsed, etc. when <devices>... <serial type="tcp">... <source mode='connect'..." If anything, the description should become more restrictive to indicate that the option shouldn't be used for smartcards, rngs, and redirdevs, but I'll save that discussion for patch 3.

>> +<pre> >> + ... >> + &lt;devices&gt; >> + &lt;serial type="tcp"&gt; >> + &lt;source mode='connect' host="127.0.0.1" service="5555" tls="yes"/&gt; >> + &lt;protocol type="raw"/&gt; >> + &lt;target port="0"/&gt; >> + &lt;/serial&gt; >> + &lt;/devices&gt; >> + ...</pre> >> + >> <h6><a name="elementsCharUDP">UDP network console</a></h6> >> >> <p> >> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng >> index 3106510..e6741bb 100644 >> --- a/docs/schemas/domaincommon.rng >> +++ b/docs/schemas/domaincommon.rng >> @@ -3453,6 +3453,11 @@ >> <ref name="virOnOff"/> >> </attribute> >> </optional> >> + <optional> >> + <attribute name="tls"> >> + <ref name="virYesNo"/> >> + </attribute> >> + </optional> >> <zeroOrMore> >> <ref name='devSeclabel'/> >> </zeroOrMore> >> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c >> index 89473db..e4fa9ad 100644 >> --- a/src/conf/domain_conf.c >> +++ b/src/conf/domain_conf.c >> @@ -1997,6 +1997,8 @@ virDomainChrSourceDefCopy(virDomainChrSourceDefPtr dest, >> >> if (VIR_STRDUP(dest->data.tcp.service, src->data.tcp.service) < 0) >> return -1; >> + >> + dest->data.tcp.haveTLS = src->data.tcp.haveTLS; >> break; >> >> case VIR_DOMAIN_CHR_TYPE_UNIX: >> @@ -10040,6 +10042,7 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def, >> char *master = NULL; >> char *slave = NULL; >> char *append = NULL; >> + char *haveTLS = NULL; >> int remaining = 0; >> >> while (cur != NULL) { >> @@ -10047,6 +10050,8 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def, >> if (xmlStrEqual(cur->name, BAD_CAST "source")) { >> if (!mode) >> mode = virXMLPropString(cur, "mode"); >> + if (!haveTLS) >> + haveTLS = virXMLPropString(cur, "tls"); >> >> switch ((virDomainChrType) def->type) { >> case VIR_DOMAIN_CHR_TYPE_FILE: >> @@ -10223,6 +10228,15 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def, >> def->data.tcp.listen = true; >> } >> >> + if (haveTLS && >> + (def->data.tcp.haveTLS = >> + virTristateBoolTypeFromString(haveTLS)) <= 0) { >> + virReportError(VIR_ERR_XML_ERROR, >> + _("unknown chardev 'tls' setting '%s'"), >> + haveTLS); >> + goto error; >> + } >> + >> if (!protocol) >> def->data.tcp.protocol = VIR_DOMAIN_CHR_TCP_PROTOCOL_RAW; >> else if ((def->data.tcp.protocol = >> @@ -10307,6 +10321,7 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def, >> VIR_FREE(append); >> VIR_FREE(logappend); >> VIR_FREE(logfile); >> + VIR_FREE(haveTLS); >> >> return remaining; >> >> @@ -21466,7 +21481,12 @@ virDomainChrSourceDefFormat(virBufferPtr buf, >> virBufferAsprintf(buf, "<source mode='%s' ", >> def->data.tcp.listen ? "bind" : "connect"); >> virBufferEscapeString(buf, "host='%s' ", def->data.tcp.host); >> - virBufferEscapeString(buf, "service='%s'/>\n", def->data.tcp.service); >> + virBufferEscapeString(buf, "service='%s'", def->data.tcp.service); >> + if (def->data.tcp.haveTLS != VIR_TRISTATE_BOOL_ABSENT) >> + virBufferAsprintf(buf, " tls='%s'", >> + virTristateBoolTypeToString(def->data.tcp.haveTLS)); >> + virBufferAddLit(buf, "/>\n"); >> + >> virBufferAsprintf(buf, "<protocol type='%s'/>\n", >> virDomainChrTcpProtocolTypeToString( >> def->data.tcp.protocol)); >> diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h >> index 04f2e40..fcadf6c 100644 >> --- a/src/conf/domain_conf.h >> +++ b/src/conf/domain_conf.h >> @@ -1094,6 +1094,7 @@ struct _virDomainChrSourceDef { >> bool listen; >> int protocol; >> bool tlscreds; >> + int haveTLS; /* enum virTristateBool */ >> } tcp; >> struct { >> char *bindHost; >> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c >> index d45a7de..f00751a 100644 >> --- a/src/qemu/qemu_command.c >> +++ b/src/qemu/qemu_command.c >> @@ -4943,7 +4943,7 @@ qemuBuildChrChardevStr(virLogManagerPtr logManager, >> if (dev->data.tcp.listen) >> virBufferAdd(&buf, nowait ? ",server,nowait" : ",server", -1); >> >> - if (qemuDomainSupportTLSChardevTCP(cfg)) { >> + if (qemuDomainSupportTLSChardevTCP(cfg, dev)) { >> char *objalias = NULL; >> >> if (qemuBuildTLSx509CommandLine(cmd, cfg->chardevTLSx509certdir, >> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c >> index 746d94f..7b518c6 100644 >> --- a/src/qemu/qemu_domain.c >> +++ b/src/qemu/qemu_domain.c >> @@ -6302,15 +6302,29 @@ qemuDomainSupportsVideoVga(virDomainVideoDefPtr video, >> >> /* qemuDomainSupportTLSChardevTCP >> * @cfg: Pointer to driver cfg >> + * @dev: Pointer to chardev source >> * >> - * Let's check if this host supports using the TLS environment for chardev. >> + * Let's check if this host and/or domain supports or desires to use >> + * the TLS environment for the passed chardev TCP. >> + * >> + * If we have an environment and as long as the domain config doesn't have >> + * the "tls='no'" property, then we assume it's desired. >> + * >> + * If the host global isn't set, but the domain chardev config is requesting >> + * to use TLS and we find what appears to be some environment configured, >> + * then let's also try. This action could fail later in QEMU if the environment >> + * isn't set up to the exact specifications. >> * >> * Returns true if we want to use TLS, false otherwise. >> */ >> bool >> -qemuDomainSupportTLSChardevTCP(virQEMUDriverConfigPtr cfg) >> +qemuDomainSupportTLSChardevTCP(virQEMUDriverConfigPtr cfg, >> + const virDomainChrSourceDef *dev) >> { >> - if (cfg->chardevTLS) >> + if (cfg->chardevTLS && dev->data.tcp.haveTLS != VIR_TRISTATE_BOOL_NO) >> + return true; >> + if (!cfg->chardevTLS && dev->data.tcp.haveTLS == VIR_TRISTATE_BOOL_YES && >> + virFileExists(cfg->chardevTLSx509certdir)) >> return true; >> return false; >> } > > So this function let's you decide whether we should try to set up *tls* for > chardev or not. It work's but I have few issues with it. > > At first I don't like that libvirt would try to do something smart and don't > even tell user about the result. This will silently ignore the *tls* > attribute if no certificate is found. In case that *tls* attribute is set > to "yes" in XML and there is no certificate file to use we shouldn't start > that domain and print an error to user. This is a boolean function - so printing an error here isn't right.

Adding something to post parse processing is possible, but there's an impact based on whether we're setting a default value for haveTLS (something I disagree with doing). Beyond that would a check go in qemuDomainDeviceDefPostParse or qemuDomainDeviceDefValidate? It's never crystal clear to me which should be used when just reading the code. Although since I see this as a "new" and "optional" value, I'd lean toward PostParse. Then there's dealing with the parseFlags that it's impacted by other decisions. I could also rationalize that someone adding "tls='yes'" to their chardev would "know" what they're doing because they read the documentation. How else would they know to have this very specific combination (unless of course 'something' set things up that way based on the assumption of how a domain is currently running). Again, IMO 'haveTLS' is new and optional. The only indication that a domain is using TLS was handled via 'tlscreds'. IIRC, the "reason" that 'tlscreds' exists and how "tls-creds" gets added to the command line is because the JSON code processing for a chardev is buried in qemu_monitor_json.c and fishing for a host configuration option at that time wasn't viable. > > Secondly this way we don't reflect the current state for live domain in the > live XML. This was probably lost during the discussion, but in general if > there is an attribute that can affect running domain we should reflect the > current state using that attribute. I know, there are some cases where we > probably don't do that and they should be fixed. > No it wasn't lost - I considered it as I see you've seen from the cover. And you're probably right regarding attributes that trigger usage of some qemu option that we don't specifically save in the status XML. That's a different rat hole. > I figure out that we cannot simply use haveTLS = cfg->chardevTLS but we > can set the haveTLS based on cfg->chardevTLS. The whole purpose of > qemuProcessPrepareDomain() is to prepare the domain definition so the > qemuBuildCommandLine() don't have to check other places to enable some > feature and not update the live definition. If the *tls* attribute is > properly set in live definition that it will be saved to status XML and > there is no need to do anything for qemuProcessReconnect. I disagree on setting haveTLS during qemuProcessReconnect based upon chardevTLS. The 'haveTLS' is an optional attribute and by setting a value I believe we end up making an assumption.

If *anything* was to be done it would be based solely on whether "tls-creds" is set on the command line of the reconnected domain. However, that too has a similar problem about setting a value for an optional attribute based upon the assumption that we know better. Again, the only indication that 'tls-creds' is on the command line was from the 'tlscreds' boolean that was set because the host configuration information was available. A domain that is running and has tls-creds will continue to have it. Altering that domain's configuration file because we add a new optional *configuration* value has no bearing on the *status* XML. When/if a configuration XML is updated, it's not checking that 'tlscreds' value to determine that at some point in history the domain used TLS because the host was configured that way.

Let's consider the bool function from above and this automagic setting being requested. Let's say we reconnect to a domain, find the 'tls-creds' set on the command line, and set 'haveTLS=YES' based solely on that. Let's say at some point in time after, someone edits their qemu.conf file and sets 'chardev_tls=0' (or comments out the 'chardev_tls=1'). In their mind, they've now disabled chardev TLS for their host and any domain they will run in the future. They stop the domain they knew was running using TLS before and restart it expecting that it won't use TLS anymore, but on restart they discover that in our infinite wisdom we have set the optional "tls='yes'" property for that chardev on that domain. Now if we 'error' out on that start like you request above, then that means they will have to edit their domain and remove the seemingly optional property. Next, let's assume they read the documentation and found that they can disable the qemu.conf value, but still have the domain chardev value if they set the "tls='yes'" property as long as they have their valid TLS directory configuration. In this case, they have made the conscious decision how they want their domain configured based on what they know is configured on the host. TBH: I take this single patch as a "feature request" add-on to the original feature request that I believe in the long run won't be used. I could be wrong, but it's a feeling. Furthermore, the purpose of any optional attribute is just that. It's optional based on some host wide setting. It's up to the consumer to decide how they should proceed, not the software to make that decision for them.