An attempt to use a validator for an empty certificate chain will
correctly fail the overall validation with the "empty certificate
chain" error propagated from x509_auto_append().
In a debug build, the call to validator_name() will attempt to call
x509_name() on a non-existent certificate, resulting in garbage in the
debug message.
Fix by checking for the special case of an empty certificate chain.
This issue does not affect non-debug builds, since validator_name() is
(as per its description) called only for debug messages.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Certificates issued by Let's Encrypt have two options for their chain
of trust: the chain can either terminate in the self-signed ISRG Root
X1 root certificate, or in an intermediate ISRG Root X1 certificate
that is signed in turn by the self-signed DST Root CA X3 root
certificate. This is a historical artifact: when Let's Encrypt first
launched as a project, the chain ending in DST Root CA X3 was used
since existing clients would not have recognised the ISRG Root X1
certificate as a trusted root certificate.
The DST Root CA X3 certificate expired in September 2021, and so is no
longer trusted by clients (such as iPXE) that validate the expiry
times of all certificates in the certificate chain.
In order to maintain usability of certificates on older Android
devices, the default certificate chain provided by Let's Encrypt still
terminates in DST Root CA X3, even though that certificate has now
expired. On newer devices which include ISRG Root X1 as a trusted
root certificate, the intermediate version of ISRG Root X1 in the
certificate chain is ignored and validation is performed as though the
chain had terminated in the self-signed ISRG Root X1 root certificate.
On older Android devices which do not include ISRG Root X1 as a
trusted root certificate, the validation succeeds since Android
chooses to ignore expiry times for root certificates and so continues
to trust the DST Root CA X3 root certificate.
This backwards compatibility hack unfortunately breaks the cross-
signing mechanism used by iPXE, which assumes that the certificate
chain will always terminate in a non-expired root certificate.
Generalise the validator's cross-signed certificate download mechanism
to walk up the certificate chain in the event of a failure, attempting
to find a replacement cross-signed certificate chain starting from the
next level up. This allows the validator to step over the expired
(and hence invalidatable) DST Root CA X3 certificate, and instead
download the cross-signed version of the ISRG Root X1 certificate.
This generalisation also gives us the ability to handle servers that
provide a full certificate chain including their root certificate:
iPXE will step over the untrusted public root certificate and attempt
to find a cross-signed version of it instead.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Record the root of trust used at the point that a certificate is
validated, redefine validation as checking a certificate against a
specific root of trust, and pass an explicit root of trust when
creating a TLS connection.
This allows a custom TLS connection to be used with a custom root of
trust, without causing any validated certificates to be treated as
valid for normal purposes.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
TLS connections will almost always create background connections to
perform cross-signed certificate downloads and OCSP checks. There is
currently no direct visibility into which checks are taking place,
which makes troubleshooting difficult in the absence of either a
packet capture or a debug build.
Use the job progress message buffer to report the current cross-signed
certificate download or OCSP status check, where applicable.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
In fully self-contained deployments it may be desirable to build iPXE
with an empty CROSSCERT source to avoid talking to external services.
Add an explicit check for this case and make validator_start_download
fail immediately if the base URI is empty.
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Provide a build option CROSSCERT in config/crypto.h to allow the
default cross-signed certificate source to be configured at build
time. The ${crosscert} setting may still be used to reconfigure the
cross-signed certificate source at runtime.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Expand the concept of the X.509 cache to provide the functionality of
a certificate store. Certificates in the store will be automatically
used to complete certificate chains where applicable.
The certificate store may be prepopulated at build time using the
CERT=... build command line option. For example:
make bin/ipxe.usb CERT=mycert1.crt,mycert2.crt
Certificates within the certificate store are not implicitly trusted;
the trust list is specified using TRUST=... as before. For example:
make bin/ipxe.usb CERT=root.crt TRUST=root.crt
This can be used to embed the full trusted root certificate within the
iPXE binary, which is potentially useful in an HTTPS-only environment
in which there is no HTTP server from which to automatically download
cross-signed certificates or other certificate chain fragments.
This usage of CERT= extends the existing use of CERT= to specify the
client certificate. The client certificate is now identified
automatically by checking for a match against the private key. For
example:
make bin/ipxe.usb CERT=root.crt,client.crt TRUST=root.crt KEY=client.key
Signed-off-by: Michael Brown <mcb30@ipxe.org>
iPXE currently allocates a copy the certificate's common name as a
string. This string is used by the TLS and CMS code to check
certificate names against an expected name, and also appears in
debugging messages.
Provide a function x509_check_name() to centralise certificate name
checking (in preparation for adding subjectAlternativeName support),
and a function x509_name() to provide a name to be used in debugging
messages, and remove the dynamically allocated string.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The fetch_setting() family of functions may currently modify the
definition of the specified setting (e.g. to add missing type
information). Clean up this interface by requiring callers to provide
an explicit buffer to contain the completed definition of the fetched
setting, if required.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
X.509 certificate processing currently produces an overwhelming amount
of debugging information. Move some of this from DBGLVL_LOG to
DBGLVL_EXTRA, to make the output more manageable.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Automatically attempt to download any required cross-signing
certificates from http://ca.ipxe.org/auto, in order to enable the use
of standard SSL certificates issued by public CAs.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
To allow for automatic download of cross-signing certificates and for
OCSP, the validation of certificates must be an asynchronous process.
Create a stub validator which uses a job-control interface to report
the result of certificate validation.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Michael Brown
Ladi Prosek