Implement trim_body support

When a message has a developer signature but is failing the signature
check, rerun it again with trim_body. If that passes, we know that the
signature is failing due to mailing list junk appended to the bottom of
the message. In that case, automatically trim the message body so we
have exactly what the developer attested and signed.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

2 files changed, 50 insertions, 3 deletions

diff --git a/b4/__init__.py b/b4/__init__.py
index 1897699..41100ad 100644
--- a/b4/__init__.py
+++ b/b4/__init__.py
@@ -1045,6 +1045,32 @@ class LoreMessage:
         # No exact domain matches, so return everything we have
         self._attestors += seenatts
 
+    def _trim_body(self) -> None:
+        # Get the length specified in the X-Developer-Signature header
+        xdsh = self.msg.get('X-Developer-Signature')
+        if not xdsh:
+            return
+        matches = re.search(r'\s+l=(\d+)', xdsh)
+        if not matches:
+            return
+        bl = int(matches.groups()[0])
+        with tempfile.TemporaryDirectory() as tfd:
+            m_out = os.path.join(tfd, 'm')
+            p_out = os.path.join(tfd, 'p')
+            cmdargs = ['mailinfo', '--encoding=UTF-8', '--no-scissors', m_out, p_out]
+            ecode, info = git_run_command(None, cmdargs, self.msg.as_bytes())
+            if not len(info.strip()):
+                return
+            with open(m_out, 'rb') as mfh:
+                bm = mfh.read()
+            with open(p_out, 'rb') as pfh:
+                bp = pfh.read()
+            bb = b''
+            for line in re.sub(rb'[\r\n]*$', b'', bm + bp).split(b'\n'):
+                bb += re.sub(rb'[\r\n]*$', b'', line) + b'\r\n'
+            if len(bb) > bl:
+                self.body = bb[:bl].decode()
+
     def _load_patatt_attestors(self) -> None:
         if not can_patatt:
             logger.debug('Message has %s headers, but can_patatt is off', DEVSIG_HDR)
@@ -1066,7 +1092,24 @@ class LoreMessage:
 
         logger.debug('Loading patatt attestations with sources=%s', str(sources))
 
-        attestations = patatt.validate_message(self.msg.as_bytes(), sources)
+        success = False
+        trim_body = False
+        while True:
+            attestations = patatt.validate_message(self.msg.as_bytes(), sources, trim_body=trim_body)
+            # Do we have any successes?
+            for attestation in attestations:
+                if attestation[0] == patatt.RES_VALID:
+                    success = True
+                    break
+            if success:
+                if trim_body:
+                    # set the body to the trimmed version
+                    self._trim_body()
+                break
+            if not success and trim_body:
+                break
+            trim_body = True
+
         for result, identity, signtime, keysrc, keyalgo, errors in attestations:
             if keysrc and keysrc.startswith('(default keyring)/'):
                 fpr = keysrc.split('/', 1)[1]
@@ -1081,7 +1124,10 @@ class LoreMessage:
                     parts = email.utils.parseaddr(uids[0])
                     identity = parts[1]
 
-            signdt = LoreAttestor.parse_ts(signtime)
+            if signtime:
+                signdt = LoreAttestor.parse_ts(signtime)
+            else:
+                signdt = None
             attestor = LoreAttestorPatatt(result, identity, signdt, keysrc, keyalgo, errors)
             self._attestors.append(attestor)
 
@@ -1105,7 +1151,8 @@ class LoreMessage:
                         # This is not critical even in hardfail
                         continue
                 elif attpolicy in ('softfail', 'hardfail'):
-                    checkmark = attestor.checkmark
+                    if not checkmark:
+                        checkmark = attestor.checkmark
                     trailers.append('%s BADSIG: %s' % (attestor.checkmark, attestor.trailer))
 
                 if attpolicy == 'hardfail':
diff --git a/patatt b/patatt
-Subproject 7754d7d35d03b462109c4a93d625f0af2138331
+Subproject d37d358c9ddd4d0972fbcd392ce26df85276794