[OE-core] [PATCH][V2] sstate: implement basic signing/validation

[Ross Burton]

To provide some element of integrity to sstate archives, allow sstate archives
to be GPG signed with a specified key (detached signature to a sidecar .sig
file), and verify the signatures when sstate archives are unpacked.

Signed-off-by: Ross Burton <ross.burton at intel.com>
---
 meta/classes/sstate.bbclass | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/meta/classes/sstate.bbclass b/meta/classes/sstate.bbclass
index 4e6afef..77313bc 100644
--- a/meta/classes/sstate.bbclass
+++ b/meta/classes/sstate.bbclass
@@ -54,6 +54,13 @@ EXTRA_STAGING_FIXMES ?= ""
 
 SIGGEN_LOCKEDSIGS_CHECK_LEVEL ?= 'error'
 
+# The GnuPG key ID and passphrase to use to sign sstate archives (or unset to
+# not sign)
+SSTATE_SIG_KEY ?= ""
+SSTATE_SIG_PASSPHRASE ?= ""
+# Whether to verify the GnUPG signatures when extracting sstate archives
+SSTATE_VERIFY_SIG ?= "0"
+
 # Specify dirs in which the shell function is executed and don't use ${B}
 # as default dirs to avoid possible race about ${B} with other task.
 sstate_create_package[dirs] = "${SSTATE_BUILDDIR}"
@@ -298,6 +305,10 @@ def sstate_installpkg(ss, d):
     d.setVar('SSTATE_INSTDIR', sstateinst)
     d.setVar('SSTATE_PKG', sstatepkg)
 
+    if bb.utils.to_boolean(d.getVar("SSTATE_VERIFY_SIG", True), False):
+        if subprocess.call(["gpg", "--verify", sstatepkg + ".sig", sstatepkg]) != 0:
+            bb.warn("Cannot verify signature on sstate package %s" % sstatepkg)
+
     for f in (d.getVar('SSTATEPREINSTFUNCS', True) or '').split() + ['sstate_unpack_package'] + (d.getVar('SSTATEPOSTUNPACKFUNCS', True) or '').split():
         bb.build.exec_func(f, d)
 
@@ -605,7 +616,8 @@ def pstaging_fetch(sstatefetch, sstatepkg, d):
     # Try a fetch from the sstate mirror, if it fails just return and
     # we will build the package
     for srcuri in ['file://{0}'.format(sstatefetch),
-                   'file://{0}.siginfo'.format(sstatefetch)]:
+                   'file://{0}.siginfo'.format(sstatefetch),
+                   'file://{0}.sig'.format(sstatefetch)]:
         localdata.setVar('SRC_URI', srcuri)
         try:
             fetcher = bb.fetch2.Fetch([srcuri], localdata, cache=False)
@@ -665,6 +677,11 @@ sstate_create_package () {
 	chmod 0664 $TFILE 
 	mv -f $TFILE ${SSTATE_PKG}
 
+	if [ -n "${SSTATE_SIG_KEY}" ]; then
+		rm -f ${SSTATE_PKG}.sig
+		echo ${SSTATE_SIG_PASSPHRASE} | gpg --batch --passphrase-fd 0 --detach-sign --local-user ${SSTATE_SIG_KEY} --output ${SSTATE_PKG}.sig ${SSTATE_PKG}
+	fi
+
 	cd ${WORKDIR}
 	rm -rf ${SSTATE_BUILDDIR}
 }
-- 
2.1.4