From 152481a026745132f8cd90fac166e6f4ecb6ea58 Mon Sep 17 00:00:00 2001
From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Sun, 10 Nov 2019 13:17:43 +0000
Subject: Fix taint-handling in rDNS name construction

---
 src/src/acl.c           |  3 +--
 src/src/dns.c           | 27 ++++++++++++++-------------
 src/src/functions.h     |  2 +-
 src/src/host.c          |  8 ++++----
 src/src/lookups/dnsdb.c |  6 +-----
 5 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/src/src/acl.c b/src/src/acl.c
index 8e34513d0..799af39c3 100644
--- a/src/src/acl.c
+++ b/src/src/acl.c
@@ -1345,8 +1345,7 @@ extension to CSA, so we allow it to be turned off for proper conformance. */
 if (string_is_ip_address(domain, NULL) != 0)
   {
   if (!dns_csa_use_reverse) return CSA_UNKNOWN;
-  dns_build_reverse(domain, target);
-  domain = target;
+  domain = dns_build_reverse(domain);
   }
 
 /* Find out if we've already done the CSA check for this domain. If we have,
diff --git a/src/src/dns.c b/src/src/dns.c
index 7736a2204..6333d3cff 100644
--- a/src/src/dns.c
+++ b/src/src/dns.c
@@ -221,16 +221,15 @@ a name that can be used to look up PTR records.
 
 Arguments:
   string     the IP address as a string
-  buffer     a suitable buffer, long enough to hold the result
 
-Returns:     nothing
+Returns:     an allocated string
 */
 
-void
-dns_build_reverse(const uschar *string, uschar *buffer)
+uschar *
+dns_build_reverse(const uschar * string)
 {
-const uschar *p = string + Ustrlen(string);
-uschar *pp = buffer;
+const uschar * p = string + Ustrlen(string);
+gstring * g = NULL;
 
 /* Handle IPv4 address */
 
@@ -240,14 +239,13 @@ if (Ustrchr(string, ':') == NULL)
   {
   for (int i = 0; i < 4; i++)
     {
-    const uschar *ppp = p;
+    const uschar * ppp = p;
     while (ppp > string && ppp[-1] != '.') ppp--;
-    Ustrncpy(pp, ppp, p - ppp);
-    pp += p - ppp;
-    *pp++ = '.';
+    g = string_catn(g, ppp, p - ppp);
+    g = string_catn(g, US".", 1);
     p = ppp - 1;
     }
-  Ustrcpy(pp, US"in-addr.arpa");
+  g = string_catn(g, US"in-addr.arpa", 12);
   }
 
 /* Handle IPv6 address; convert to binary so as to fill out any
@@ -257,6 +255,8 @@ abbreviation in the textual form. */
 else
   {
   int v6[4];
+
+  g = string_get_tainted(32, is_tainted(string));
   (void)host_aton(string, v6);
 
   /* The original specification for IPv6 reverse lookup was to invert each
@@ -265,8 +265,8 @@ else
 
   for (int i = 3; i >= 0; i--)
     for (int j = 0; j < 32; j += 4)
-      pp += sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
-  Ustrcpy(pp, US"ip6.arpa.");
+      g = string_fmt_append(g, "%x.", (v6[i] >> j) & 15);
+  g = string_catn(g, US"ip6.arpa.", 9);
 
   /* Another way of doing IPv6 reverse lookups was proposed in conjunction
   with A6 records. However, it fell out of favour when they did. The
@@ -290,6 +290,7 @@ else
 
   }
 #endif
+return string_from_gstring(g);
 }
 
 
diff --git a/src/src/functions.h b/src/src/functions.h
index eca8e798d..f4fcd1e19 100644
--- a/src/src/functions.h
+++ b/src/src/functions.h
@@ -197,7 +197,7 @@ extern BOOL    dkim_transport_write_message(transport_ctx *,
 #endif
 extern dns_address *dns_address_from_rr(dns_answer *, dns_record *);
 extern int     dns_basic_lookup(dns_answer *, const uschar *, int);
-extern void    dns_build_reverse(const uschar *, uschar *);
+extern uschar *dns_build_reverse(const uschar *);
 extern time_t  dns_expire_from_soa(dns_answer *, int);
 extern void    dns_init(BOOL, BOOL, BOOL);
 extern BOOL    dns_is_aa(const dns_answer *);
diff --git a/src/src/host.c b/src/src/host.c
index aa142eb9b..3361d5912 100644
--- a/src/src/host.c
+++ b/src/src/host.c
@@ -1646,7 +1646,6 @@ int old_pool, rc;
 int sep = 0;
 uschar *save_hostname;
 uschar **aliases;
-uschar buffer[256];
 uschar *ordername;
 const uschar *list = host_lookup_order;
 dns_answer * dnsa = store_get_dns_answer();
@@ -1672,13 +1671,14 @@ if (f.running_in_test_harness &&
 /* Do lookups directly in the DNS or via gethostbyaddr() (or equivalent), in
 the order specified by the host_lookup_order option. */
 
-while ((ordername = string_nextinlist(&list, &sep, buffer, sizeof(buffer))))
+while ((ordername = string_nextinlist(&list, &sep, NULL, 0)))
   {
   if (strcmpic(ordername, US"bydns") == 0)
     {
+    uschar * name = dns_build_reverse(sender_host_address);
+
     dns_init(FALSE, FALSE, FALSE);    /* dnssec ctrl by dns_dnssec_ok glbl */
-    dns_build_reverse(sender_host_address, buffer);
-    rc = dns_lookup_timerwrap(dnsa, buffer, T_PTR, NULL);
+    rc = dns_lookup_timerwrap(dnsa, name, T_PTR, NULL);
 
     /* The first record we come across is used for the name; others are
     considered to be aliases. We have to scan twice, in order to find out the
diff --git a/src/src/lookups/dnsdb.c b/src/src/lookups/dnsdb.c
index 1cf8df739..94809e5d8 100644
--- a/src/src/lookups/dnsdb.c
+++ b/src/src/lookups/dnsdb.c
@@ -312,7 +312,6 @@ if (!outsep2) switch(type)
 
 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
   {
-  uschar rbuffer[256];
   int searchtype = type == T_CSA ? T_SRV :         /* record type we want */
                    type == T_MXH ? T_MX :
                    type == T_ZNS ? T_NS : type;
@@ -325,10 +324,7 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 
   if ((type == T_PTR || type == T_CSA) &&
       string_is_ip_address(domain, NULL) != 0)
-    {
-    dns_build_reverse(domain, rbuffer);
-    domain = rbuffer;
-    }
+    domain = dns_build_reverse(domain);
 
   do
     {
-- 
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