From beb15dae3f15ff993556b44897bed035d543c683 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Wed, 19 Mar 2014 16:18:12 +0000
Subject: [PATCH] base.m4, vhost.m4: Very hacky DH field-size limitation.

We can't set `tls_dh_min_bits' from an expansion.  So set up multiple
transports for different thresholds.
---
 base.m4  | 20 +++++++++++++-------
 vhost.m4 |  5 +++--
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/base.m4 b/base.m4
index 523e475..4a925df 100644
--- a/base.m4
+++ b/base.m4
@@ -348,9 +348,11 @@ SECTION(transports)m4_dnl
 ## A standard transport for remote delivery.  By default, try to do TLS, and
 ## don't worry too much if it's not very secure: the alternative is sending
 ## in plaintext anyway.  But all of this can be overridden from the
-## `domains.conf' file.
-smtp:
-	driver = smtp
+## `domains.conf' file.  Annoyingly, the `tls_dh_min_bits' setting isn't
+## expanded before use, so we can't set it the obvious way.  Instead, encode
+## it into the transport name.  This is very unpleasant, of course.
+m4_define(<:SMTP_TRANS_DHBITS:>,
+	<:driver = smtp
 	hosts_try_auth = *
 	hosts_require_tls = DOMKV(tls-peer-ca, {*}{})
 	hosts_require_auth = \
@@ -366,10 +368,14 @@ smtp:
 				 {$value} \
 				 {${expand:$value}}}} \
 		      {CONF_acceptable_ciphers})
-	## Can't set this to an expansion. :-(
-	m4_dnl tls_dh_min_bits = DOMKV(dh-min-bits, {$value}{1020})
-	tls_dh_min_bits = 1020
-	tls_tempfail_tryclear = true
+	tls_dh_min_bits = $1
+	tls_tempfail_tryclear = true:>)m4_dnl
+smtp:
+	SMTP_TRANS_DHBITS(1020)
+smtp_dhbits_1024:
+	SMTP_TRANS_DHBITS(1020)
+smtp_dhbits_2048:
+	SMTP_TRANS_DHBITS(2046)
 
 ## Transport to a local SMTP server; use TLS and perform client
 ## authentication.
diff --git a/vhost.m4 b/vhost.m4
index b4cfb01..41bc715 100644
--- a/vhost.m4
+++ b/vhost.m4
@@ -40,7 +40,8 @@ m4_define(<:VHOST_USER:>,
 
 SECTION(routers, route)m4_dnl
 ## If we're a front-end for some other domain, or we have special information
-## about the domain, then pass stuff along as instructed.
+## about the domain, then pass stuff along as instructed.  The hack for the
+## `transport' is very nasty; see the commentary for `smtp'.
 virtual_route:
 	driver = manualroute
 	self = fail
@@ -48,7 +49,7 @@ virtual_route:
 	condition = DOMKV(route, {true}{false})
 	route_data = <;DOMKV(route)
 	same_domain_copy_routing = true
-	transport = smtp
+	transport = DOMKV(tls-min-dh-bits, {smtp_dhbits_$value}{smtp})
 	no_more
 
 SECTION(routers, virtual)m4_dnl
-- 
2.11.0