CLI: rework PGP verification

The verification of PGP signatures had some flaws and didn't work, because
the Python API and the GPG interface have changed. Inline signatures were
not detected, because of a comparison of string and byte array. And even
after this the code failed, because `sig.status` is no longer available.

Author: jo-so-nx

bmaptools/CLI.py

@@ -128,74 +128,58 @@ def open_block_device(path):
     return NamedFile(file_obj, path)
 
 
-def report_verification_results(context, sigs):
-    """
-    This is a helper function which reports the GPG signature verification
-    results. The 'context' argument is the gpg context object, and the 'sigs'
-    argument contains the results of the 'gpg.verify()' function.
+def verify_bmap_signature(args, bmap_obj, bmap_path):
     """
+    Verify GPG signature of the bmap file if it is present. The signature may
+    be in a separate file (detached) or it may be inside the bmap file itself
+    (clearsign signature).
 
-    import gpg
-
-    for sig in sigs:
-        if (sig.summary & gpg.constants.SIGSUM_VALID) != 0:
-            key = context.get_key(sig.fpr)
-            author = "%s <%s>" % (key.uids[0].name, key.uids[0].email)
-            log.info(
-                "successfully verified bmap file signature of %s "
-                "(fingerprint %s)" % (author, sig.fpr)
-            )
-        else:
-            error_out(
-                "signature verification failed (fingerprint %s): %s\n"
-                "Either fix the problem or use --no-sig-verify to "
-                "disable signature verification",
-                sig.fpr,
-                sig.status[2].lower(),
-            )
-
+    If user specifies the --bmap-sig option, the signature is assumed to be
+    detached and is taken from the user-specified file. Otherwise, this
+    function verifies whether the bmap file has clearsign signature, and if
+    not, it tries to automatically discover the detached signature by searching
+    for a ".sig" or ".asc" file at the same path and with the same basename as
+    the bmap file. This function then verifies the signature and reports the
+    results.
 
-def verify_detached_bmap_signature(args, bmap_obj, bmap_path):
-    """
-    This is a helper function for 'verify_bmap_signature()' which handles the
-    detached signature case.
+    In case of the clearsign signature, the bmap file has "invalid" format,
+    meaning that the proper bmap XML contents is in the GPG clearsign
+    container. The XML contents has to be extracted from the container before
+    further processing. And this is be done even if user specified the
+    --no-sig-verify option. This function returns an open file object with the
+    extracted XML bmap file contents in this case. Otherwise, this function
+    returns None.
     """
 
-    if args.no_sig_verify:
+    if not bmap_obj:
         return None
 
-    if args.bmap_sig:
+    clearsign_marker = b"-----BEGIN PGP SIGNED MESSAGE-----"
+    buf = bmap_obj.read(len(clearsign_marker))
+    bmap_obj.seek(0)
+
+    if buf == clearsign_marker:
+        log.info("discovered inline signature")
+        detached_sig = None
+    elif args.no_sig_verify:
+        return None
+    elif args.bmap_sig:
         try:
-            sig_obj = TransRead.TransRead(args.bmap_sig)
+            detached_sig = TransRead.TransRead(args.bmap_sig)
         except TransRead.Error as err:
             error_out("cannot open bmap signature file '%s':\n%s", args.bmap_sig, err)
-        sig_path = args.bmap_sig
     else:
         # Check if there is a stand-alone signature file
         try:
-            sig_path = bmap_path + ".asc"
-            sig_obj = TransRead.TransRead(sig_path)
+            detached_sig = TransRead.TransRead(bmap_path + ".asc")
         except TransRead.Error:
             try:
-                sig_path = bmap_path + ".sig"
-                sig_obj = TransRead.TransRead(sig_path)
+                detached_sig = TransRead.TransRead(bmap_path + ".sig")
             except TransRead.Error:
-                # No signatures found
+                # No detached signatures found
                 return None
 
-        log.info("discovered signature file for bmap '%s'" % sig_path)
-
-    # If the stand-alone signature file is not local, make a local copy
-    if sig_obj.is_url:
-        try:
-            tmp_obj = tempfile.NamedTemporaryFile("wb+")
-        except IOError as err:
-            error_out("cannot create a temporary file for the signature:\n%s", err)
-
-        shutil.copyfileobj(sig_obj, tmp_obj)
-        tmp_obj.seek(0)
-        sig_obj.close()
-        sig_obj = tmp_obj
+        log.info("discovered signature file for bmap '%s'" % detached_sig.name)
 
     try:
         import gpg
@@ -207,124 +191,70 @@ def verify_detached_bmap_signature(args, bmap_obj, bmap_path):
         )
 
     try:
-        context = gpg.Context()
-        signature = io.FileIO(sig_obj.name)
-        signed_data = io.FileIO(bmap_obj.name)
-        sigs = context.verify(signed_data, signature, None)[1].signatures
-    except gpg.errors.GPGMEError as err:
-        error_out(
-            "failure when trying to verify GPG signature: %s\n"
-            'Make sure file "%s" has proper GPG format',
-            err.getstring(),
-            sig_path,
-        )
-    except gpg.errors.BadSignatures as err:
-        error_out("discovered a BAD GPG signature: %s\n", sig_path)
-
-    sig_obj.close()
-
-    if len(sigs) == 0:
-        log.warning(
-            'the "%s" signature file does not actually contain '
-            "any valid signatures" % sig_path
-        )
-    else:
-        report_verification_results(context, sigs)
-
-    return None
-
+        bmap_data = bmap_obj.read()
+        bmap_obj.seek(0)
 
-def verify_clearsign_bmap_signature(args, bmap_obj):
-    """
-    This is a helper function for 'verify_bmap_signature()' which handles the
-    clarsign signature case.
-    """
-
-    if args.bmap_sig:
-        error_out(
-            "the bmap file has clearsign format and already contains "
-            "the signature, so --bmap-sig option should not be used"
-        )
-
-    try:
-        import gpg
-    except ImportError:
-        error_out(
-            'cannot verify the signature because the python "gpg"'
-            "module is not installed on your system\nCannot extract "
-            "block map from the bmap file which has clearsign format, "
-            "please, install the module"
-        )
+        if detached_sig:
+            det_sig_data = detached_sig.read()
+            detached_sig.close()
+        else:
+            det_sig_data = None
 
-    try:
         context = gpg.Context()
-        signature = io.FileIO(bmap_obj.name)
-        plaintext = io.BytesIO()
-        sigs = context.verify(plaintext, signature, None)
+        plaintext, sigs = context.verify(bmap_data, det_sig_data)
+        sigs = sigs.signatures
     except gpg.errors.GPGMEError as err:
         error_out(
             "failure when trying to verify GPG signature: %s\n"
             "make sure the bmap file has proper GPG format",
             err[2].lower(),
         )
     except gpg.errors.BadSignatures as err:
-        error_out("discovered a BAD GPG signature: %s\n", sig_path)
+        error_out(
+            "discovered a BAD GPG signature: %s\n",
+            detached_sig.name if detached_sig else bmap_obj.name
+        )
 
     if not args.no_sig_verify:
         if len(sigs) == 0:
             log.warning(
+                'the "%s" signature file does not actually contain '
+                "any valid signatures" % detached_sig.name if detached_sig
+                else
                 "the bmap file clearsign signature does not actually "
                 "contain any valid signatures"
             )
         else:
-            report_verification_results(context, sigs)
+            for sig in sigs:
+                if (sig.summary & gpg.constants.SIGSUM_VALID) != 0:
+                    key = context.get_key(sig.fpr)
+                    author = "%s <%s>" % (key.uids[0].name, key.uids[0].email)
+                    log.info(
+                        "successfully verified bmap file signature of %s "
+                        "(fingerprint %s)" % (author, sig.fpr)
+                    )
+                else:
+                    error_out(
+                        "signature verification failed (fingerprint %s)\n"
+                        "Either fix the problem or use --no-sig-verify to "
+                        "disable signature verification",
+                        sig.fpr,
+                    )
+
+    if detached_sig:
+        # for detached signatures we are done
+        return None
 
     try:
-        tmp_obj = tempfile.TemporaryFile("w+")
+        tmp_obj = tempfile.TemporaryFile("w+b")
     except IOError as err:
         error_out("cannot create a temporary file for bmap:\n%s", err)
 
-    tmp_obj.write(plaintext.getvalue())
+    tmp_obj.write(plaintext)
     tmp_obj.seek(0)
     return tmp_obj
 
 
-def verify_bmap_signature(args, bmap_obj, bmap_path):
-    """
-    Verify GPG signature of the bmap file if it is present. The signature may
-    be in a separate file (detached) or it may be inside the bmap file itself
-    (clearsign signature).
-
-    If user specifies the --bmap-sig option, the signature is assumed to be
-    detached and is taken from the user-specified file. Otherwise, this
-    function verifies whether the bmap file has clearsign signature, and if
-    not, it tries to automatically discover the detached signature by searching
-    for a ".sig" or ".asc" file at the same path and with the same basename as
-    the bmap file. This function then verifies the signature and reports the
-    results.
-
-    In case of the clearsign signature, the bmap file has "invalid" format,
-    meaning that the proper bmap XML contents is in the GPG clearsign
-    container. The XML contents has to be extracted from the container before
-    further processing. And this is be done even if user specified the
-    --no-sig-verify option. This function returns an open file object with the
-    extracted XML bmap file contents in this case. Otherwise, this function
-    returns None.
-    """
-
-    if not bmap_obj:
-        return None
-
-    clearsign_marker = "-----BEGIN PGP SIGNED MESSAGE-----"
-    buf = bmap_obj.read(len(clearsign_marker))
-    bmap_obj.seek(0)
-
-    if buf == clearsign_marker:
-        return verify_clearsign_bmap_signature(args, bmap_obj)
-    else:
-        return verify_detached_bmap_signature(args, bmap_obj, bmap_path)
-
-
 def find_and_open_bmap(args):
     """
     This is a helper function for 'open_files()' which discovers and opens the