[PATCH v2 2/4] util/repair: identify and repair "Mixed Up" mangled messages
Daniel Kahn Gillmor
dkg at fifthhorseman.net
Thu May 30 10:27:05 PDT 2019
This patch implements a functional identification and repair process
for "Mixed Up" MIME messages as described in
https://tools.ietf.org/html/draft-dkg-openpgp-pgpmime-message-mangling-00#section-4.1
The detection test is not entirely complete, in that it does not
verify the contents of the latter two message subparts, but this is
probably safe to skip, because those two parts are unlikely to be
readable anyway, and the only part we are effectively omitting (the
first subpart) is guaranteed to be empty anyway, so its removal can be
reversed if you want to do so. I've left FIXMEs in the code so that
anyone excited about adding these additional checks can see where to
put them in.
I'll use this functionality in the next two patches.
Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
---
util/Makefile.local | 1 +
util/repair.c | 101 ++++++++++++++++++++++++++++++++++++++++++++
util/repair.h | 22 ++++++++++
3 files changed, 124 insertions(+)
create mode 100644 util/repair.c
create mode 100644 util/repair.h
diff --git a/util/Makefile.local b/util/Makefile.local
index 46f8af3a..f5d72f79 100644
--- a/util/Makefile.local
+++ b/util/Makefile.local
@@ -6,6 +6,7 @@ extra_cflags += -I$(srcdir)/$(dir)
libnotmuch_util_c_srcs := $(dir)/xutil.c $(dir)/error_util.c $(dir)/hex-escape.c \
$(dir)/string-util.c $(dir)/talloc-extra.c $(dir)/zlib-extra.c \
$(dir)/util.c $(dir)/gmime-extra.c $(dir)/crypto.c \
+ $(dir)/repair.c \
$(dir)/unicode-util.c
libnotmuch_util_modules := $(libnotmuch_util_c_srcs:.c=.o)
diff --git a/util/repair.c b/util/repair.c
new file mode 100644
index 00000000..56d6c5b5
--- /dev/null
+++ b/util/repair.c
@@ -0,0 +1,101 @@
+/* notmuch - Not much of an email program, (just index and search)
+ *
+ * Copyright © 2019 Daniel Kahn Gillmor
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see https://www.gnu.org/licenses/ .
+ *
+ * Authors: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
+ */
+
+#include <stdbool.h>
+#include "repair.h"
+
+/* see
+ * https://tools.ietf.org/html/draft-dkg-openpgp-pgpmime-message-mangling-00#section-4.1.1 */
+static bool
+_notmuch_is_mixed_up_mangled (GMimeObject *part)
+{
+ GMimeMultipart *mpart = NULL;
+ GMimeObject *first, *second, *third = NULL;
+ char *prelude_string = NULL;
+ bool prelude_is_empty;
+
+ if (! g_mime_content_type_is_type (g_mime_object_get_content_type (part),
+ "multipart", "mixed"))
+ return false;
+ if (! GMIME_IS_MULTIPART (part))
+ return false;
+ mpart = GMIME_MULTIPART (part);
+ if (mpart == NULL)
+ return false;
+ if (g_mime_multipart_get_count (mpart) != 3)
+ return false;
+ first = g_mime_multipart_get_part (mpart, 0);
+ if (! g_mime_content_type_is_type (g_mime_object_get_content_type (first),
+ "text", "plain"))
+ return false;
+ if (! GMIME_IS_TEXT_PART (first))
+ return false;
+ second = g_mime_multipart_get_part (mpart, 1);
+ if (! g_mime_content_type_is_type (g_mime_object_get_content_type (second),
+ "application", "pgp-encrypted"))
+ return false;
+ third = g_mime_multipart_get_part (mpart, 2);
+ if (! g_mime_content_type_is_type (g_mime_object_get_content_type (third),
+ "application", "octet-stream"))
+ return false;
+
+ /* Is first subpart length 0? */
+ prelude_string = g_mime_text_part_get_text (GMIME_TEXT_PART (first));
+ prelude_is_empty = ! (strcmp ("", prelude_string));
+ g_free (prelude_string);
+ if (! prelude_is_empty)
+ return false;
+
+ /* FIXME: after decoding and stripping whitespace, is second
+ * subpart just "Version: 1" ? */
+
+ /* FIXME: can we determine that third subpart is *only* PGP
+ * encrypted data? I tried g_mime_part_get_openpgp_data () but
+ * found https://github.com/jstedfast/gmime/issues/60 */
+
+ return true;
+}
+
+
+/* see
+ * https://tools.ietf.org/html/draft-dkg-openpgp-pgpmime-message-mangling-00#section-4.1.2 */
+GMimeObject*
+_notmuch_repair_mixed_up_mangled (GMimeObject *part)
+{
+ GMimeMultipart *mpart = NULL, *mpart_ret = NULL;
+ GMimeObject *ret = NULL;
+
+ if (! _notmuch_is_mixed_up_mangled (part))
+ return NULL;
+ mpart = GMIME_MULTIPART (part);
+ ret = GMIME_OBJECT (g_mime_multipart_encrypted_new ());
+ if (ret == NULL)
+ return NULL;
+ mpart_ret = GMIME_MULTIPART (ret);
+ if (mpart_ret == NULL) {
+ g_object_unref (ret);
+ return NULL;
+ }
+ g_mime_object_set_content_type_parameter (ret, "protocol", "application/pgp-encrypted");
+
+ g_mime_multipart_insert (mpart_ret, 0, g_mime_multipart_get_part (mpart, 1));
+ g_mime_multipart_insert (mpart_ret, 1, g_mime_multipart_get_part (mpart, 2));
+ return ret;
+}
diff --git a/util/repair.h b/util/repair.h
new file mode 100644
index 00000000..a16644fc
--- /dev/null
+++ b/util/repair.h
@@ -0,0 +1,22 @@
+#ifndef _REPAIR_H
+#define _REPAIR_H
+
+#include "gmime-extra.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Detecting and repairing "Mixed-Up MIME mangling". see
+ * https://tools.ietf.org/html/draft-dkg-openpgp-pgpmime-message-mangling-00#section-4.1
+ * If this returns NULL, the message was probably not "Mixed up". If
+ * it returns non-NULL, then there is a newly-allocated MIME part that
+ * represents the repaired version. The caller is responsible for
+ * ensuring that any returned object is freed with g_object_unref. */
+GMimeObject*
+_notmuch_repair_mixed_up_mangled (GMimeObject *part);
+
+#ifdef __cplusplus
+}
+#endif
+#endif
--
2.20.1
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