lib-src/pop.c may attempt to connect to the wrong host

lib-src/pop.c may attempt to connect to the wrong host

[Jonathan Kamens]

This bug report will be sent to the Free Software Foundation,
not to your local site managers!
Please write in English, because the Emacs maintainers do not have
translators to read other languages for them.

Your bug report will be posted to the bug-gnu-emacs@gnu.org mailing list,
and to the gnu.emacs.bug news group.

In GNU Emacs 21.2.1 (i386-redhat-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-04-08 on porky.devel.redhat.com
configured using `configure  i386-redhat-linux --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --with-gcc --with-pop --with-sound'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

TAhe patch appended below was made against 20.7, but I believe that it
will apply cleanly, or almost cleanly, against the current source tree
as well.

The code in socket_connection in lib-src/pop.c results the host name
of the POP host, then uses getservbyname() to look up the port number,
then iterates through the addresses of the POP host and attempts to
connect to each of them in turn.

The problem with this approach is that getservbyname() may call
gethostbyname() or gethostbyaddr(), e.g., if nsswitch.com says to use
LDAP for service lookups, and thus replace the address information
about the POP host with the address information for some other host,
thus causing the POP connection to go to the wrong host.  I have
seen this failure mode.

The fix for this is to wait to resolve the POP host name until
immediately before trying to connect to it.  I've attached a patch.

  jik

--- lib-src/pop.c.orig	Sun May 12 20:23:32 2002
+++ lib-src/pop.c	Sun May 12 20:27:21 2002
@@ -1067,17 +1067,6 @@
   }
 #endif
 
-  do
-    {
-      hostent = gethostbyname (host);
-      try_count++;
-      if ((! hostent) && ((h_errno != TRY_AGAIN) || (try_count == 5)))
-	{
-	  strcpy (pop_error, "Could not determine POP server's address");
-	  return (-1);
-	}
-    } while (! hostent);
-
   bzero ((char *) &addr, sizeof (addr));
   addr.sin_family = AF_INET;
 
@@ -1127,6 +1116,17 @@
       return (-1);
 	  
     }
+
+  do
+    {
+      hostent = gethostbyname (host);
+      try_count++;
+      if ((! hostent) && ((h_errno != TRY_AGAIN) || (try_count == 5)))
+	{
+	  strcpy (pop_error, "Could not determine POP server's address");
+	  return (-1);
+	}
+    } while (! hostent);
 
   while (*hostent->h_addr_list)
     {