sstate: Allow validation of sstate singatures against list of keys

Allow a user to validate sstate objects against a list of keys, instead
of just any known key in the user's keychain.

(From OE-Core rev: 52ba0c5e6e2e3d5d01dc3f01404f0ab1bb29b3b5)

Signed-off-by: Daniel McGregor <daniel.mcgregor@vecima.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sstate.bbclass

@@ -116,6 +116,9 @@ SSTATE_SIG_KEY ?= ""
 SSTATE_SIG_PASSPHRASE ?= ""
 # Whether to verify the GnUPG signatures when extracting sstate archives
 SSTATE_VERIFY_SIG ?= "0"
+# List of signatures to consider valid.
+SSTATE_VALID_SIGS ??= ""
+SSTATE_VALID_SIGS[vardepvalue] = ""
 
 SSTATE_HASHEQUIV_METHOD ?= "oe.sstatesig.OEOuthashBasic"
 SSTATE_HASHEQUIV_METHOD[doc] = "The fully-qualified function used to calculate \
@@ -372,7 +375,7 @@ def sstate_installpkg(ss, d):
             bb.warn("No signature file for sstate package %s, skipping acceleration..." % sstatepkg)
             return False
         signer = get_signer(d, 'local')
-        if not signer.verify(sstatepkg + '.sig'):
+        if not signer.verify(sstatepkg + '.sig', d.getVar("SSTATE_VALID_SIGS")):
             bb.warn("Cannot verify signature on sstate package %s, skipping acceleration..." % sstatepkg)
             return False
 

meta/lib/oe/gpg_sign.py

@@ -109,16 +109,33 @@ class LocalSigner(object):
             bb.fatal("Could not get gpg version: %s" % e)
 
 
-    def verify(self, sig_file):
+    def verify(self, sig_file, valid_sigs = ''):
         """Verify signature"""
-        cmd = self.gpg_cmd + ["--verify", "--no-permission-warning"]
+        cmd = self.gpg_cmd + ["--verify", "--no-permission-warning", "--status-fd", "1"]
         if self.gpg_path:
             cmd += ["--homedir", self.gpg_path]
 
         cmd += [sig_file]
-        status = subprocess.call(cmd)
-        ret = False if status else True
-        return ret
+        status = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        # Valid if any key matches if unspecified
+        if not valid_sigs:
+            ret = False if status.returncode else True
+            return ret
+
+        import re
+        goodsigs = []
+        sigre = re.compile(r'^\[GNUPG:\] GOODSIG (\S+)\s(.*)$')
+        for l in status.stdout.decode("utf-8").splitlines():
+            s = sigre.match(l)
+            if s:
+                goodsigs += [s.group(1)]
+
+        for sig in valid_sigs.split():
+            if sig in goodsigs:
+                return True
+        if len(goodsigs):
+            bb.warn('No accepted signatures found. Good signatures found: %s.' % ' '.join(goodsigs))
+        return False
 
 
 def get_signer(d, backend):