1 files changed, 501 insertions, 0 deletions

diff --git a/src/plugins/mail-crypt/mail-crypt-plugin.c b/src/plugins/mail-crypt/mail-crypt-plugin.c
new file mode 100644
index 0000000..69c3b59
--- /dev/null
+++ b/src/plugins/mail-crypt/mail-crypt-plugin.c
@@ -0,0 +1,501 @@
+/* Copyright (c) 2015-2018 Dovecot authors, see the included COPYING file */
+
+/* FIXME: cache handling could be useful to move to Dovecot core, so that if
+   we're using this plugin together with zlib plugin there would be just one
+   cache. */
+
+#include "lib.h"
+#include "ioloop.h"
+#include "randgen.h"
+#include "module-dir.h"
+#include "str.h"
+#include "safe-mkstemp.h"
+#include "istream.h"
+#include "istream-decrypt.h"
+#include "istream-seekable.h"
+#include "ostream.h"
+#include "ostream-encrypt.h"
+#include "mail-user.h"
+#include "mail-copy.h"
+#include "index-storage.h"
+#include "index-mail.h"
+#include "mail-crypt-common.h"
+#include "mail-crypt-key.h"
+#include "mail-crypt-plugin.h"
+#include "sha2.h"
+#include "dcrypt-iostream.h"
+#include "hex-binary.h"
+
+struct mail_crypt_mailbox {
+	union mailbox_module_context module_ctx;
+	struct dcrypt_public_key *pub_key;
+};
+
+const char *mail_crypt_plugin_version = DOVECOT_ABI_VERSION;
+
+#define MAIL_CRYPT_MAIL_CONTEXT(obj) \
+	MODULE_CONTEXT_REQUIRE(obj, mail_crypt_mail_module)
+#define MAIL_CRYPT_CONTEXT(obj) \
+	MODULE_CONTEXT_REQUIRE(obj, mail_crypt_storage_module)
+#define MAIL_CRYPT_USER_CONTEXT(obj) \
+	MODULE_CONTEXT(obj, mail_crypt_user_module)
+#define MAIL_CRYPT_USER_CONTEXT_REQUIRE(obj) \
+	MODULE_CONTEXT_REQUIRE(obj, mail_crypt_user_module)
+
+static MODULE_CONTEXT_DEFINE_INIT(mail_crypt_user_module,
+				  &mail_user_module_register);
+static MODULE_CONTEXT_DEFINE_INIT(mail_crypt_storage_module,
+				  &mail_storage_module_register);
+static MODULE_CONTEXT_DEFINE_INIT(mail_crypt_mail_module,
+				  &mail_module_register);
+
+struct mail_crypt_user *mail_crypt_get_mail_crypt_user(struct mail_user *user)
+{
+	return MAIL_CRYPT_USER_CONTEXT(user);
+}
+
+static bool mail_crypt_is_stream_encrypted(struct istream *input)
+{
+	const unsigned char *data = NULL;
+	size_t size;
+
+	if (i_stream_read_data(input, &data, &size,
+				sizeof(IOSTREAM_CRYPT_MAGIC)) <= 0) {
+		return FALSE;
+	}
+
+	if (memcmp(data, IOSTREAM_CRYPT_MAGIC,
+		      sizeof(IOSTREAM_CRYPT_MAGIC)) != 0) {
+		return FALSE;
+	}
+	return TRUE;
+}
+
+static void mail_crypt_cache_close(struct mail_crypt_user *muser)
+{
+	struct mail_crypt_cache *cache = &muser->cache;
+
+	timeout_remove(&cache->to);
+	i_stream_unref(&cache->input);
+	i_zero(cache);
+}
+
+static struct istream *
+mail_crypt_cache_open(struct mail_crypt_user *muser, struct mail *mail,
+		      struct istream *input)
+{
+	struct mail_crypt_cache *cache = &muser->cache;
+	struct istream *inputs[2];
+	string_t *temp_prefix = t_str_new(128);
+
+	mail_crypt_cache_close(muser);
+
+	input->seekable = FALSE;
+	inputs[0] = input;
+	inputs[1] = NULL;
+	mail_user_set_get_temp_prefix(temp_prefix, mail->box->storage->user->set);
+	input = i_stream_create_seekable_path(inputs,
+				i_stream_get_max_buffer_size(inputs[0]),
+				str_c(temp_prefix));
+	i_stream_unref(&inputs[0]);
+
+	if (mail->uid > 0) {
+		cache->to = timeout_add(MAIL_CRYPT_MAIL_CACHE_EXPIRE_MSECS,
+				mail_crypt_cache_close, muser);
+		cache->box = mail->box;
+		cache->uid = mail->uid;
+		cache->input = input;
+		/* index-mail wants the stream to be destroyed at close, so create
+		   a new stream instead of just increasing reference. */
+		return i_stream_create_limit(cache->input, UOFF_T_MAX);
+	}
+
+	return input;
+}
+
+static int mail_crypt_istream_get_private_key(const char *pubkey_digest,
+			   struct dcrypt_private_key **priv_key_r,
+			   const char **error_r,
+			   void *context)
+{
+	/* mailbox_crypt_search_all_private_keys requires error_r != NULL */
+	i_assert(error_r != NULL);
+	int ret;
+	struct mail *_mail = context;
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT_REQUIRE(_mail->box->storage->user);
+
+	*priv_key_r = mail_crypt_global_key_find(&muser->global_keys,
+						 pubkey_digest);
+	if (*priv_key_r != NULL) {
+		dcrypt_key_ref_private(*priv_key_r);
+		return 1;
+	}
+
+	struct mail_namespace *ns = mailbox_get_namespace(_mail->box);
+
+	if (ns->type == MAIL_NAMESPACE_TYPE_SHARED) {
+		ret = mail_crypt_box_get_shared_key(_mail->box, pubkey_digest,
+						    priv_key_r, error_r);
+		/* priv_key_r is already referenced */
+	} else if (ns->type != MAIL_NAMESPACE_TYPE_PUBLIC) {
+		ret = mail_crypt_get_private_key(_mail->box, pubkey_digest,
+						 FALSE, FALSE, priv_key_r,
+						 error_r);
+		/* priv_key_r is already referenced */
+	} else {
+		*error_r = "Public emails cannot have keys";
+		ret = -1;
+	}
+
+	i_assert(ret <= 0 || *priv_key_r != NULL);
+
+	return ret;
+}
+
+static int
+mail_crypt_istream_opened(struct mail *_mail, struct istream **stream)
+{
+	struct mail_private *mail = (struct mail_private *)_mail;
+	struct mail_user *user = _mail->box->storage->user;
+	struct mail_crypt_user *muser = MAIL_CRYPT_USER_CONTEXT_REQUIRE(user);
+	struct mail_crypt_cache *cache = &muser->cache;
+	union mail_module_context *mmail = MAIL_CRYPT_MAIL_CONTEXT(mail);
+	struct istream *input;
+
+	if (_mail->uid > 0 && cache->uid == _mail->uid && cache->box == _mail->box) {
+		/* use the cached stream. when doing partial reads it should
+		   already be seeked into the wanted offset. */
+		i_stream_unref(stream);
+		i_stream_seek(cache->input, 0);
+		*stream = i_stream_create_limit(cache->input, UOFF_T_MAX);
+		return mmail->super.istream_opened(_mail, stream);
+	}
+
+	/* decryption is the outmost stream, so add it before others
+	   (e.g. zlib) */
+	if (!mail_crypt_is_stream_encrypted(*stream))
+		return mmail->super.istream_opened(_mail, stream);
+
+	input = *stream;
+	*stream = i_stream_create_decrypt_callback(input,
+				mail_crypt_istream_get_private_key, _mail);
+	i_stream_unref(&input);
+
+	*stream = mail_crypt_cache_open(muser, _mail, *stream);
+	return mmail->super.istream_opened(_mail, stream);
+}
+
+static void mail_crypt_close(struct mail *_mail)
+{
+	struct mail_private *mail = (struct mail_private *)_mail;
+	union mail_module_context *mmail = MAIL_CRYPT_MAIL_CONTEXT(mail);
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT_REQUIRE(_mail->box->storage->user);
+	struct mail_crypt_cache *cache = &muser->cache;
+	uoff_t size;
+
+	if (_mail->uid > 0 && cache->uid == _mail->uid && cache->box == _mail->box) {
+		/* make sure we have read the entire email into the seekable
+		   stream (which causes the original input stream to be
+		   unrefed). we can't safely keep the original input stream
+		   open after the mail is closed. */
+		if (i_stream_get_size(cache->input, TRUE, &size) < 0)
+			mail_crypt_cache_close(muser);
+	}
+	mmail->super.close(_mail);
+}
+
+static void mail_crypt_mail_allocated(struct mail *_mail)
+{
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT(_mail->box->storage->user);
+	if (muser == NULL) return;
+
+	struct mail_private *mail = (struct mail_private *)_mail;
+	struct mail_vfuncs *v = mail->vlast;
+	union mail_module_context *mmail;
+
+	mmail = p_new(mail->pool, union mail_module_context, 1);
+	mmail->super = *v;
+	mail->vlast = &mmail->super;
+
+	v->istream_opened = mail_crypt_istream_opened;
+	v->close = mail_crypt_close;
+	MODULE_CONTEXT_SET_SELF(mail, mail_crypt_mail_module, mmail);
+}
+
+static int mail_crypt_mail_save_finish(struct mail_save_context *ctx)
+{
+	struct mailbox *box = ctx->transaction->box;
+	union mailbox_module_context *zbox = MAIL_CRYPT_CONTEXT(box);
+	struct istream *input;
+
+	if (zbox->super.save_finish(ctx) < 0)
+		return -1;
+
+	/* we're here only if mail-crypt plugin is disabled. we want to make
+	   sure that even though we're saving an unencrypted mail, the mail
+	   can't be faked to look like an encrypted mail. */
+	if (mail_get_stream(ctx->dest_mail, NULL, NULL, &input) < 0)
+		return -1;
+
+	if (mail_crypt_is_stream_encrypted(input)) {
+		mail_storage_set_error(box->storage, MAIL_ERROR_NOTPOSSIBLE,
+			"Saving mails encrypted by client isn't supported");
+		return -1;
+	}
+	return 0;
+}
+
+static int
+mail_crypt_mail_save_begin(struct mail_save_context *ctx,
+			   struct istream *input)
+{
+	const char *pubid;
+	struct mailbox *box = ctx->transaction->box;
+	struct mail_crypt_mailbox *mbox = MAIL_CRYPT_CONTEXT(box);
+	struct mail_crypt_user *muser = MAIL_CRYPT_USER_CONTEXT(box->storage->user);
+
+	enum io_stream_encrypt_flags enc_flags = 0;
+	if (muser != NULL) {
+		if (muser->save_version == 1) {
+			enc_flags = IO_STREAM_ENC_VERSION_1;
+		} else if (muser->save_version == 2) {
+			enc_flags = IO_STREAM_ENC_INTEGRITY_AEAD;
+		} else {
+			i_assert(muser->save_version == 0);
+		}
+	}
+
+	if (mbox->module_ctx.super.save_begin(ctx, input) < 0)
+		return -1;
+
+	if (enc_flags == 0)
+		return 0;
+
+	struct dcrypt_public_key *pub_key;
+	if (muser->global_keys.public_key != NULL)
+		pub_key = muser->global_keys.public_key;
+	else if (mbox->pub_key != NULL)
+		pub_key = mbox->pub_key;
+	else {
+		const char *error;
+		int ret;
+
+		if ((ret = mail_crypt_box_get_public_key(box, &pub_key,
+							 &error)) <= 0)
+		{
+			struct dcrypt_keypair pair;
+
+			if (ret < 0) {
+				mail_storage_set_error(box->storage,
+					MAIL_ERROR_PARAMS,
+					t_strdup_printf("get_public_key(%s) failed: %s",
+							mailbox_get_vname(box),
+							error));
+				return ret;
+			}
+
+			if (muser->save_version < 2) {
+				mail_storage_set_error(box->storage,
+                                        MAIL_ERROR_PARAMS,
+                                        t_strdup_printf("generate_keypair(%s) failed: "
+                                                        "unsupported save_version=%d",
+                                                        mailbox_get_vname(box),
+                                                        muser->save_version));
+                                return -1;
+			}
+
+			if (mail_crypt_box_generate_keypair(box, &pair, NULL,
+							    &pubid, &error) < 0) {
+				mail_storage_set_error(box->storage,
+					MAIL_ERROR_PARAMS,
+					t_strdup_printf("generate_keypair(%s) failed: %s",
+							mailbox_get_vname(box),
+							error));
+				return -1;
+			}
+			pub_key = pair.pub;
+			dcrypt_key_unref_private(&pair.priv);
+
+		}
+		mbox->pub_key = pub_key;
+	}
+
+	/* encryption is the outermost layer (zlib etc. are inside) */
+	struct ostream *output = o_stream_create_encrypt(ctx->data.output,
+			MAIL_CRYPT_ENC_ALGORITHM, pub_key, enc_flags);
+
+	o_stream_unref(&ctx->data.output);
+	ctx->data.output = output;
+	o_stream_cork(ctx->data.output);
+	return 0;
+}
+
+static int
+mail_crypt_mailbox_copy(struct mail_save_context *ctx, struct mail *mail)
+{
+	struct mailbox *dest_box = ctx->transaction->box;
+	struct mail_crypt_mailbox *mbox = MAIL_CRYPT_CONTEXT(dest_box);
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT(dest_box->storage->user);
+
+	bool raw_copy;
+	if (mailbox_backends_equal(dest_box, mail->box)) {
+		/* Copy to same box always have identical crypt profile */
+		raw_copy = TRUE;
+	} else if (strcmp(dest_box->storage->user->username,
+			  mail->box->storage->user->username) != 0) {
+		/* Always consider copies between different users unsafe
+		   as they may have different encryption level and/or
+		   different global keys */
+		raw_copy = FALSE;
+	} else {
+		/* Within same user, consider safe only the case where
+		   encryption is enabled and keys are global. */
+		raw_copy = muser != NULL &&
+			   muser->save_version != 0 &&
+			   muser->global_keys.public_key != NULL;
+	}
+
+	return raw_copy ?
+	       mbox->module_ctx.super.copy(ctx, mail) :
+	       mail_storage_copy(ctx, mail);
+}
+
+static void mail_crypt_mailbox_close(struct mailbox *box)
+{
+	struct mail_crypt_mailbox *mbox = MAIL_CRYPT_CONTEXT(box);
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT(box->storage->user);
+
+	if (mbox->pub_key != NULL)
+		dcrypt_key_unref_public(&mbox->pub_key);
+	if (muser != NULL && muser->cache.box == box)
+		mail_crypt_cache_close(muser);
+	mbox->module_ctx.super.close(box);
+}
+
+static void mail_crypt_mailbox_allocated(struct mailbox *box)
+{
+	struct mailbox_vfuncs *v = box->vlast;
+	struct mail_crypt_user *muser =
+		MAIL_CRYPT_USER_CONTEXT(box->storage->user);
+	struct mail_crypt_mailbox *mbox;
+	enum mail_storage_class_flags class_flags = box->storage->class_flags;
+
+	mbox = p_new(box->pool, struct mail_crypt_mailbox, 1);
+	mbox->module_ctx.super = *v;
+	box->vlast = &mbox->module_ctx.super;
+	v->close = mail_crypt_mailbox_close;
+
+	MODULE_CONTEXT_SET(box, mail_crypt_storage_module, mbox);
+
+	if ((class_flags & MAIL_STORAGE_CLASS_FLAG_BINARY_DATA) != 0) {
+		v->save_begin = mail_crypt_mail_save_begin;
+		v->copy = mail_crypt_mailbox_copy;
+
+		if (muser == NULL || muser->save_version == 0)
+			v->save_finish = mail_crypt_mail_save_finish;
+	}
+}
+
+static void mail_crypt_mail_user_deinit(struct mail_user *user)
+{
+	struct mail_crypt_user *muser = MAIL_CRYPT_USER_CONTEXT_REQUIRE(user);
+
+	mail_crypt_key_cache_destroy(&muser->key_cache);
+	mail_crypt_global_keys_free(&muser->global_keys);
+	mail_crypt_cache_close(muser);
+	muser->module_ctx.super.deinit(user);
+}
+
+static void mail_crypt_mail_user_created(struct mail_user *user)
+{
+	struct mail_user_vfuncs *v = user->vlast;
+	struct mail_crypt_user *muser;
+	const char *error = NULL;
+
+	muser = p_new(user->pool, struct mail_crypt_user, 1);
+	muser->module_ctx.super = *v;
+	user->vlast = &muser->module_ctx.super;
+
+	const char *curve = mail_user_plugin_getenv(user, "mail_crypt_curve");
+	buffer_t *tmp = t_str_new(64);
+	if (curve == NULL || *curve == '\0') {
+		e_debug(user->event, "mail_crypt_plugin: mail_crypt_curve setting "
+			"missing - generating EC keys disabled");
+	} else if (!dcrypt_name2oid(curve, tmp, &error)) {
+		user->error = p_strdup_printf(user->pool,
+			"mail_crypt_plugin: "
+			"invalid mail_crypt_curve setting %s: %s",
+			curve, error);
+	} else {
+		muser->curve = p_strdup(user->pool, curve);
+	}
+
+	const char *version = mail_user_plugin_getenv(user,
+			"mail_crypt_save_version");
+
+	if (version == NULL || *version == '\0') {
+		user->error = p_strdup_printf(user->pool,
+				"mail_crypt_plugin: "
+				"mail_crypt_save_version setting missing");
+	} else if (version[0] == '0') {
+		muser->save_version = 0;
+	} else if (version[0] == '1') {
+		muser->save_version = 1;
+	} else if (version[0] == '2') {
+		muser->save_version = 2;
+	} else {
+		user->error = p_strdup_printf(user->pool,
+				"mail_crypt_plugin: Invalid "
+				"mail_crypt_save_version %s: use 0, 1, or 2 ",
+				version);
+	}
+
+	if (mail_crypt_global_keys_load(user, "mail_crypt_global",
+					&muser->global_keys, FALSE, &error) < 0) {
+		user->error = p_strdup_printf(user->pool,
+				"mail_crypt_plugin: %s", error);
+	}
+
+	v->deinit = mail_crypt_mail_user_deinit;
+	MODULE_CONTEXT_SET(user, mail_crypt_user_module, muser);
+}
+
+static struct mail_storage_hooks mail_crypt_mail_storage_hooks = {
+	.mail_user_created = mail_crypt_mail_user_created,
+	.mail_allocated = mail_crypt_mail_allocated
+};
+
+static struct mail_storage_hooks mail_crypt_mail_storage_hooks_post = {
+	.mailbox_allocated = mail_crypt_mailbox_allocated
+};
+
+static struct module crypto_post_module = {
+	.path = "lib95_mail_crypt_plugin.so"
+};
+
+void mail_crypt_plugin_init(struct module *module)
+{
+	const char* error;
+	if (!dcrypt_initialize("openssl", NULL, &error))
+		i_fatal("dcrypt_initialize(): %s", error);
+	mail_storage_hooks_add(module, &mail_crypt_mail_storage_hooks);
+	/* when this plugin is loaded, there's the potential chance for
+	   mixed delivery between encrypted and non-encrypted recipients.
+	   The mail_crypt_mailbox_allocated() hook ensures encrypted
+	   content isn't copied as such into cleartext recipients
+	   (and the other way around) */
+	mail_storage_hooks_add_forced(&crypto_post_module,
+				      &mail_crypt_mail_storage_hooks_post);
+	mail_crypt_key_register_mailbox_internal_attributes();
+}
+
+void mail_crypt_plugin_deinit(void)
+{
+	mail_storage_hooks_remove(&mail_crypt_mail_storage_hooks);
+	mail_storage_hooks_remove(&mail_crypt_mail_storage_hooks_post);
+}