From 7986de66296c7e73d39c485b317f9163ac520019 Mon Sep 17 00:00:00 2001
From: Scott Kitterman <scott@kitterman.com>
Date: Mon, 23 Sep 2019 11:52:17 -0400
Subject: [PATCH]  - Catch more ascii encoding errors to improve resilience
 against bad data    (LP: #1844189)

---
 CHANGES                   |  2 ++
 dkimpy_milter/__init__.py | 37 ++++++++++++++++++++++++++++++-------
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/CHANGES b/CHANGES
index b201c36..44ea9c2 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,8 @@
    as verifying works correctly
  - Fix variable initialization so mailformed mails missing body From do not
    cause a traceback (LP: #1844161)
+ - Catch more ascii encoding errors to improve resilience against bad data
+   (LP: #1844189)
 
 1.0.1 2019-02-11
  * Reorder milter start and dropping privileges so permissions on Unix socket
diff --git a/dkimpy_milter/__init__.py b/dkimpy_milter/__init__.py
index a450b26..fa114db 100644
--- a/dkimpy_milter/__init__.py
+++ b/dkimpy_milter/__init__.py
@@ -141,7 +141,11 @@ class dkimMilter(Milter.Base):
         elif lname == 'authentication-results':
             self.arheaders.append(val)
         if self.fp:
-            self.fp.write("%s: %s\n" % (name, val))
+            try:
+                self.fp.write("%s: %s\n" % (name, val))
+            except:
+                # Don't choke on header fields with garbage in them.
+                pass
         return Milter.CONTINUE
 
     @Milter.noreply
@@ -255,6 +259,7 @@ class dkimMilter(Milter.Base):
 
     def check_dkim(self, txt):
         res = False
+        self.header_a = None
         for y in range(self.has_dkim):  # Verify _ALL_ the signatures
             d = dkim.DKIM(txt)
             try:
@@ -281,9 +286,20 @@ class dkimMilter(Milter.Base):
                 self.dkim_comment = str(x)
                 if milterconfig.get('Syslog'):
                     syslog.syslog("check_dkim: {0}".format(x))
-            self.header_i = d.signature_fields.get(b'i')
-            self.header_d = d.signature_fields.get(b'd')
-            self.header_a = d.signature_fields.get(b'a')
+            try:
+                self.header_i = d.signature_fields.get(b'i')
+            except TypeError as x:
+                self.header_i = None
+            try:
+                self.header_d = d.signature_fields.get(b'd')
+                self.header_a = d.signature_fields.get(b'a')
+            except Exception as x:
+                self.dkim_comment = str(x)
+                if milterconfig.get('Syslog'):
+                    syslog.syslog("check_dkim: {0}".format(x))
+                self.header_d = None
+            if not self.header_a:
+                self.header_a = 'rsa-sha256'
             if res:
                 if (milterconfig.get('Syslog') and
                         (milterconfig.get('SyslogSuccess') or
@@ -303,20 +319,27 @@ class dkimMilter(Milter.Base):
                         syslog.syslog('DKIM: Fail (saved as {0})'
                                       .format(fname))
                 else:
-                    syslog.syslog('DKIM: Fail ({0})'.format(d.domain.lower()))
+                    if milterconfig.get('Syslog'):
+                        if d.domain:
+                            syslog.syslog('DKIM: Fail ({0})'
+                                          .format(d.domain.lower()))
+                        else:
+                            syslog.syslog('DKIM: Fail, unextractable domain')
             if res:
                 result = 'pass'
             else:
                 result = 'fail'
             res = False
-            self.arresults.append(
-                authres.DKIMAuthenticationResult(result=result,
+            if self.header_d:
+                self.arresults.append(
+                    authres.DKIMAuthenticationResult(result=result,
                                                  header_i=self.header_i,
                                                  header_d=self.header_d,
                                                  header_a=self.header_a,
                                                  result_comment=
                                                  self.dkim_comment)
             )
+            self.header_a = None
         return