ph10 2006/02/07 16:36:25 GMT
Modified files:
exim-doc/doc-txt ChangeLog
exim-src/src host.c
exim-test/stderr 0419 0499 1006
exim-test/stdout 0430
Log:
Always do explicit A/AAAA lookups; no longer make use of the additional
RR section from MX/SRV lookups.
Revision Changes Path
1.286 +10 -0 exim/exim-doc/doc-txt/ChangeLog
1.21 +33 -179 exim/exim-src/src/host.c
1.2 +4 -0 exim/exim-test/stderr/0419
1.2 +5 -0 exim/exim-test/stderr/0499
1.2 +5 -0 exim/exim-test/stderr/1006
1.2 +2 -2 exim/exim-test/stdout/0430
Index: ChangeLog
===================================================================
RCS file: /home/cvs/exim/exim-doc/doc-txt/ChangeLog,v
retrieving revision 1.285
retrieving revision 1.286
diff -u -r1.285 -r1.286
--- ChangeLog 7 Feb 2006 14:20:58 -0000 1.285
+++ ChangeLog 7 Feb 2006 16:36:25 -0000 1.286
@@ -1,4 +1,4 @@
-$Cambridge: exim/exim-doc/doc-txt/ChangeLog,v 1.285 2006/02/07 14:20:58 ph10 Exp $
+$Cambridge: exim/exim-doc/doc-txt/ChangeLog,v 1.286 2006/02/07 16:36:25 ph10 Exp $
Change log file for Exim from version 4.21
-------------------------------------------
@@ -88,6 +88,16 @@
PH/15 Minor change to Makefile for building test_host (undocumented testing
feature).
+
+PH/16 As discussed on the list in Nov/Dec: Exim no longer looks at the
+ additional section of a DNS packet that returns MX or SRV records.
+ Instead, it always explicitly searches for A/AAAA records. This avoids
+ major problems that occur when a DNS server includes only records of one
+ type (A or AAAA) in an MX/SRV packet. A byproduct of this change has
+ fixed another bug: if SRV records were looked up and the corresponding
+ address records were *not* found in the additional section, the port
+ values from the SRV records were lost.
+
Exim version 4.60
Index: host.c
===================================================================
RCS file: /home/cvs/exim/exim-src/src/host.c,v
retrieving revision 1.20
retrieving revision 1.21
diff -u -r1.20 -r1.21
--- host.c 7 Feb 2006 11:19:00 -0000 1.20
+++ host.c 7 Feb 2006 16:36:25 -0000 1.21
@@ -1,4 +1,4 @@
-/* $Cambridge: exim/exim-src/src/host.c,v 1.20 2006/02/07 11:19:00 ph10 Exp $ */
+/* $Cambridge: exim/exim-src/src/host.c,v 1.21 2006/02/07 16:36:25 ph10 Exp $ */
/*************************************************
* Exim - an Internet mail transport agent *
@@ -2192,10 +2192,10 @@
* Fill in a host address from the DNS *
*************************************************/
-/* Given a host item, with its name and mx fields set, and its address field
-set to NULL, fill in its IP address from the DNS. If it is multi-homed, create
-additional host items for the additional addresses, copying all the other
-fields, and randomizing the order.
+/* Given a host item, with its name, port and mx fields set, and its address
+field set to NULL, fill in its IP address from the DNS. If it is multi-homed,
+create additional host items for the additional addresses, copying all the
+other fields, and randomizing the order.
On IPv6 systems, A6 records are sought first (but only if support for A6 is
configured - they may never become mainstream), then AAAA records are sought,
@@ -2250,7 +2250,6 @@
#endif
host->address = host->name;
- host->port = PORT_NONE;
return HOST_FOUND;
}
@@ -2360,7 +2359,6 @@
if (strcmpic(host->name, rr->name) != 0)
host->name = string_copy_dnsdomain(rr->name);
host->address = da->address;
- host->port = PORT_NONE;
host->sort_key = host->mx * 1000 + random_number(500) + randoffset;
host->status = hstatus_unknown;
host->why = hwhy_unknown;
@@ -2395,10 +2393,9 @@
if (new_sort_key < host->sort_key)
{
- *next = *host;
+ *next = *host; /* Copies port */
host->next = next;
host->address = da->address;
- host->port = PORT_NONE;
host->sort_key = new_sort_key;
if (thishostlast == host) thishostlast = next; /* Local last */
if (*lastptr == host) *lastptr = next; /* Global last */
@@ -2415,10 +2412,9 @@
if (new_sort_key < h->next->sort_key) break;
h = h->next;
}
- *next = *h;
+ *next = *h; /* Copies port */
h->next = next;
next->address = da->address;
- next->port = PORT_NONE;
next->sort_key = new_sort_key;
if (h == thishostlast) thishostlast = next; /* Local last */
if (h == *lastptr) *lastptr = next; /* Global last */
@@ -2439,15 +2435,15 @@
/*************************************************
-* Find IP addresses and names for host via DNS *
+* Find IP addresses and host names via DNS *
*************************************************/
-/* The input is a host_item structure with the name filled in and the address
-field set to NULL. This may be in a chain of other host items. The lookup may
-result in more than one IP address, in which case we must created new host
-blocks for the additional addresses, and insert them into the chain. The
-original name may not be fully qualified. Use the fully_qualified_name argument
-to return the official name, as returned by the resolver.
+/* The input is a host_item structure with the name field filled in and the
+address field set to NULL. This may be in a chain of other host items. The
+lookup may result in more than one IP address, in which case we must created
+new host blocks for the additional addresses, and insert them into the chain.
+The original name may not be fully qualified. Use the fully_qualified_name
+argument to return the official name, as returned by the resolver.
Arguments:
host point to initial host item
@@ -2638,7 +2634,7 @@
{
int precedence;
int weight = 0; /* For SRV records */
- int port = PORT_NONE; /* For SRV records */
+ int port = PORT_NONE;
uschar *s; /* MUST be unsigned for GETSHORT */
uschar data[256];
@@ -2879,175 +2875,33 @@
} /* Move on to the next host */
}
-/* Now we have to ensure addresses exist for all the hosts. We have ensured
-above that the names in the host items are all unique. The addresses may have
-been returned in the additional data section of the DNS query. Because it is
-more expensive to scan the returned DNS records (because you have to expand the
-names) we do a single scan over them, and multiple scans of the chain of host
-items (which is typically only 3 or 4 long anyway.) Add extra host items for
-multi-homed hosts. */
-
-for (rr = dns_next_rr(&dnsa, &dnss, RESET_ADDITIONAL);
- rr != NULL;
- rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
- {
- dns_address *da;
- int status = hstatus_unknown;
- int why = hwhy_unknown;
- int randoffset;
-
- if (rr->type != T_A
- #if HAVE_IPV6
- && ( disable_ipv6 ||
- (
- rr->type != T_AAAA
- #ifdef SUPPORT_A6
- && rr->type != T_A6
- #endif
- )
- )
- #endif
- ) continue;
-
- /* Find the first host that matches this record's name. If there isn't
- one, move on to the next RR. */
-
- for (h = host; h != last->next; h = h->next)
- { if (strcmpic(h->name, rr->name) == 0) break; }
- if (h == last->next) continue;
-
- /* For IPv4 addresses, add 500 to the random part of the sort key, to ensure
- they sort after IPv6 addresses. */
-
- randoffset = (rr->type == T_A)? 500 : 0;
-
- /* Get the list of textual addresses for this RR. There may be more than one
- if it is an A6 RR. Then loop to handle multiple addresses from an A6 record.
- If there are none, nothing will get done - the record is ignored. */
-
- for (da = dns_address_from_rr(&dnsa, rr); da != NULL; da = da->next)
- {
- /* Set status for an ignorable host. */
-
- #ifndef STAND_ALONE
- if (ignore_target_hosts != NULL &&
- verify_check_this_host(&ignore_target_hosts, NULL, h->name,
- da->address, NULL) == OK)
- {
- DEBUG(D_host_lookup)
- debug_printf("ignored host %s [%s]\n", h->name, da->address);
- status = hstatus_unusable;
- why = hwhy_ignored;
- }
- #endif
-
- /* If the address is already set for this host, it may be that
- we just have a duplicate DNS record. Alternatively, this may be
- a multi-homed host. Search all items with the same host name
- (they will all be together) and if this address is found, skip
- to the next RR. */
-
- if (h->address != NULL)
- {
- int new_sort_key;
- host_item *thishostlast;
- host_item *hh = h;
-
- do
- {
- if (hh->address != NULL && Ustrcmp(CS da->address, hh->address) == 0)
- goto DNS_NEXT_RR; /* Need goto to escape from inner loop */
- thishostlast = hh;
- hh = hh->next;
- }
- while (hh != last->next && strcmpic(hh->name, rr->name) == 0);
-
- /* We have a multi-homed host, since we have a new address for
- an existing name. Create a copy of the current item, and give it
- the new address. RRs can be in arbitrary order, but one is supposed
- to randomize the addresses of multi-homed hosts, so compute a new
- sorting key and do that. [Latest SMTP RFC says not to randomize multi-
- homed hosts, but to rely on the resolver. I'm not happy about that -
- caching in the resolver will not rotate as often as the name server
- does.] */
-
- new_sort_key = h->mx * 1000 + random_number(500) + randoffset;
- hh = store_get(sizeof(host_item));
-
- /* New address goes first: insert the new block after the first one
- (so as not to disturb the original pointer) but put the new address
- in the original block. */
-
- if (new_sort_key < h->sort_key)
- {
- *hh = *h; /* Note: copies the port */
- h->next = hh;
- h->address = da->address;
- h->sort_key = new_sort_key;
- h->status = status;
- h->why = why;
- }
-
- /* Otherwise scan down the addresses for this host to find the
- one to insert after. */
-
- else
- {
- while (h != thishostlast)
- {
- if (new_sort_key < h->next->sort_key) break;
- h = h->next;
- }
- *hh = *h; /* Note: copies the port */
- h->next = hh;
- hh->address = da->address;
- hh->sort_key = new_sort_key;
- hh->status = status;
- hh->why = why;
- }
-
- if (h == last) last = hh; /* Inserted after last */
- }
-
- /* The existing item doesn't have its address set yet, so just set it.
- Ensure that an IPv4 address gets its sort key incremented in case an IPv6
- address is found later. */
-
- else
- {
- h->address = da->address; /* Port should be set already */
- h->status = status;
- h->why = why;
- h->sort_key += randoffset;
- }
- } /* Loop for addresses extracted from one RR */
-
- /* Carry on to the next RR. It would be nice to be able to be able to stop
- when every host on the list has an address, but we can't be sure there won't
- be an additional address for a multi-homed host further down the list, so
- we have to continue to the end. */
-
- DNS_NEXT_RR: continue;
- }
-
-/* Set the default yield to failure */
-
-yield = HOST_FIND_FAILED;
-
-/* If we haven't found all the addresses in the additional section, we
-need to search for A or AAAA records explicitly. The names shouldn't point to
-CNAMES, but we use the general lookup function that handles them, just
-in case. If any lookup gives a soft error, change the default yield.
+/* Now we have to find IP addresses for all the hosts. We have ensured above
+that the names in all the host items are unique. Before release 4.61 we used to
+process records from the additional section in the DNS packet that returned the
+MX or SRV records. However, a DNS name server is free to drop any resource
+records from the additional section. In theory, this has always been a
+potential problem, but it is exacerbated by the advent of IPv6. If a host had
+several IPv4 addresses and some were not in the additional section, at least
+Exim would try the others. However, if a host had both IPv4 and IPv6 addresses
+and all the IPv4 (say) addresses were absent, Exim would try only for a IPv6
+connection, and never try an IPv4 address. When there was only IPv4
+connectivity, this was a disaster that did in practice occur.
+
+So, from release 4.61 onwards, we always search for A and AAAA records
+explicitly. The names shouldn't point to CNAMES, but we use the general lookup
+function that handles them, just in case. If any lookup gives a soft error,
+change the default yield.
For these DNS lookups, we must disable qualify_single and search_parents;
otherwise invalid host names obtained from MX or SRV records can cause trouble
if they happen to match something local. */
-dns_init(FALSE, FALSE);
+yield = HOST_FIND_FAILED; /* Default yield */
+dns_init(FALSE, FALSE); /* Disable qualify_single and search_parents */
for (h = host; h != last->next; h = h->next)
{
- if (h->address != NULL || h->status == hstatus_unusable) continue;
+ if (h->address != NULL) continue; /* Inserted by a multihomed host */
rc = set_address_from_dns(h, &last, ignore_target_hosts, allow_mx_to_ip, NULL);
if (rc != HOST_FOUND)
{
Index: 0419
===================================================================
RCS file: /home/cvs/exim/exim-test/stderr/0419,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- 0419 7 Feb 2006 10:47:31 -0000 1.1
+++ 0419 7 Feb 2006 16:36:25 -0000 1.2
@@ -24,6 +24,10 @@
domain = mxt13.test.ex
DNS lookup of mxt13.test.ex (MX) using fakens
DNS lookup of mxt13.test.ex (MX) succeeded
+DNS lookup of other1.test.ex (A) using fakens
+DNS lookup of other1.test.ex (A) succeeded
+DNS lookup of other2.test.ex (A) using fakens
+DNS lookup of other2.test.ex (A) succeeded
other1.test.ex in "!mxt13.test.ex : !other1.test.ex : *.test.ex"? no (matched "!other1.test.ex")
other1.test.ex in hosts_treat_as_local? no (end of list)
other2.test.ex in "!mxt13.test.ex : !other1.test.ex : *.test.ex"? yes (matched "*.test.ex")
Index: 0499
===================================================================
RCS file: /home/cvs/exim/exim-test/stderr/0499,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- 0499 7 Feb 2006 10:47:31 -0000 1.1
+++ 0499 7 Feb 2006 16:36:25 -0000 1.2
@@ -17,6 +17,8 @@
checking domains
DNS lookup of mxt1.test.ex (MX) using fakens
DNS lookup of mxt1.test.ex (MX) succeeded
+DNS lookup of eximtesthost.test.ex (A) using fakens
+DNS lookup of eximtesthost.test.ex (A) succeeded
local host has lowest MX
host_find_bydns yield = HOST_FOUND_LOCAL (3); returned hosts:
eximtesthost.test.ex ip4.ip4.ip4.ip4 MX=5
@@ -25,6 +27,9 @@
checking "condition"
DNS lookup of mxt1.test.ex (MX) using fakens
DNS lookup of mxt1.test.ex (MX) succeeded
+DNS lookup of eximtesthost.test.ex-AAAA: using cached value DNS_NODATA
+DNS lookup of eximtesthost.test.ex (A) using fakens
+DNS lookup of eximtesthost.test.ex (A) succeeded
local host has lowest MX
host_find_bydns yield = HOST_FOUND_LOCAL (3); returned hosts:
eximtesthost.test.ex ip4.ip4.ip4.ip4 MX=5
Index: 1006
===================================================================
RCS file: /home/cvs/exim/exim-test/stderr/1006,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- 1006 7 Feb 2006 10:47:31 -0000 1.1
+++ 1006 7 Feb 2006 16:36:25 -0000 1.2
@@ -6,6 +6,9 @@
DNS lookup of 46.test.ex (AAAA) succeeded
DNS lookup of 46.test.ex (A) using fakens
DNS lookup of 46.test.ex (A) succeeded
+DNS lookup of 46.test.ex (AAAA) succeeded
+DNS lookup of 46.test.ex (A) using fakens
+DNS lookup of 46.test.ex (A) succeeded
DNS lookup of v6.test.ex (MX) using fakens
DNS lookup of v6.test.ex (MX) gave NO_DATA
returning DNS_NODATA
@@ -19,6 +22,8 @@
admin user
DNS lookup of mx46.test.ex (MX) using fakens
DNS lookup of mx46.test.ex (MX) succeeded
+DNS lookup of 46.test.ex (A) using fakens
+DNS lookup of 46.test.ex (A) succeeded
DNS lookup of 46.test.ex (A) using fakens
DNS lookup of 46.test.ex (A) succeeded
DNS lookup of v6.test.ex (MX) using fakens
Index: 0430
===================================================================
RCS file: /home/cvs/exim/exim-test/stdout/0430,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- 0430 7 Feb 2006 10:47:37 -0000 1.1
+++ 0430 7 Feb 2006 16:36:25 -0000 1.2
@@ -31,10 +31,10 @@
host ten-1.test.ex [V4NET.0.0.1]
y@???
router = r2, transport = t1
- host ten-6.test.ex [V4NET.0.0.6]
- host ten-1.test.ex [V4NET.0.0.1]
host ten-2.test.ex [V4NET.0.0.2] MX=5
host ten-3.test.ex [V4NET.0.0.3] MX=6
+ host ten-6.test.ex [V4NET.0.0.6]
+ host ten-1.test.ex [V4NET.0.0.1]
x@???
router = r2, transport = t1
host ten-6.test.ex [V4NET.0.0.6]
