Restore TCP wrappers support

Support for TCP wrappers was dropped in OpenSSH 6.7.  See this message
and thread:

  https://lists.mindrot.org/pipermail/openssh-unix-dev/2014-April/032497.html

It is true that this reduces preauth attack surface in sshd.  On the
other hand, this support seems to be quite widely used, and abruptly
dropping it (from the perspective of users who don't read
openssh-unix-dev) could easily cause more serious problems in practice.

It's not entirely clear what the right long-term answer for Debian is,
but it at least probably doesn't involve dropping this feature shortly
before a freeze.

Forwarded: not-needed
Last-Update: 2014-10-07

Patch-Name: restore-tcp-wrappers.patch

3 files changed, 89 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 5f1ff740f..5d720f77a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1481,6 +1481,62 @@ AC_ARG_WITH([skey],
         ]
 )
 
+# Check whether user wants TCP wrappers support
+TCPW_MSG="no"
+AC_ARG_WITH([tcp-wrappers],
+        [  --with-tcp-wrappers[[=PATH]] Enable tcpwrappers support (optionally in PATH)],
+        [
+                if test "x$withval" != "xno" ; then
+                        saved_LIBS="$LIBS"
+                        saved_LDFLAGS="$LDFLAGS"
+                        saved_CPPFLAGS="$CPPFLAGS"
+                        if test -n "${withval}" && \
+                            test "x${withval}" != "xyes"; then
+                                if test -d "${withval}/lib"; then
+                                        if test -n "${need_dash_r}"; then
+                                                LDFLAGS="-L${withval}/lib -R${withval}/lib ${LDFLAGS}"
+                                        else
+                                                LDFLAGS="-L${withval}/lib ${LDFLAGS}"
+                                        fi
+                                else
+                                        if test -n "${need_dash_r}"; then
+                                                LDFLAGS="-L${withval} -R${withval} ${LDFLAGS}"
+                                        else
+                                                LDFLAGS="-L${withval} ${LDFLAGS}"
+                                        fi
+                                fi
+                                if test -d "${withval}/include"; then
+                                        CPPFLAGS="-I${withval}/include ${CPPFLAGS}"
+                                else
+                                        CPPFLAGS="-I${withval} ${CPPFLAGS}"
+                                fi
+                        fi
+                        LIBS="-lwrap $LIBS"
+                        AC_MSG_CHECKING([for libwrap])
+                        AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <tcpd.h>
+int deny_severity = 0, allow_severity = 0;
+                                ]], [[
+        hosts_access(0);
+                                ]])], [
+                                        AC_MSG_RESULT([yes])
+                                        AC_DEFINE([LIBWRAP], [1],
+                                                [Define if you want
+                                                TCP Wrappers support])
+                                        SSHDLIBS="$SSHDLIBS -lwrap"
+                                        TCPW_MSG="yes"
+                                ], [
+                                        AC_MSG_ERROR([*** libwrap missing])
+                                
+                        ])
+                        LIBS="$saved_LIBS"
+                fi
+        ]
+)
+
 # Check whether user wants to use ldns
 LDNS_MSG="no"
 AC_ARG_WITH(ldns,
@@ -5003,6 +5059,7 @@ echo "                 KerberosV support: $KRB5_MSG"
 echo "                   SELinux support: $SELINUX_MSG"
 echo "                 Smartcard support: $SCARD_MSG"
 echo "                     S/KEY support: $SKEY_MSG"
+echo "              TCP Wrappers support: $TCPW_MSG"
 echo "              MD5 password support: $MD5_MSG"
 echo "                   libedit support: $LIBEDIT_MSG"
 echo "  Solaris process contract support: $SPC_MSG"
diff --git a/sshd.8 b/sshd.8
index 6c521f23e..589841fcc 100644
--- a/sshd.8
+++ b/sshd.8
@@ -880,6 +880,12 @@ the user's home directory becomes accessible.
 This file should be writable only by the user, and need not be
 readable by anyone else.
 .Pp
+.It Pa /etc/hosts.allow
+.It Pa /etc/hosts.deny
+Access controls that should be enforced by tcp-wrappers are defined here.
+Further details are described in
+.Xr hosts_access 5 .
+.Pp
 .It Pa /etc/hosts.equiv
 This file is for host-based authentication (see
 .Xr ssh 1 ) .
@@ -986,6 +992,7 @@ The content of this file is not sensitive; it can be world-readable.
 .Xr ssh-keygen 1 ,
 .Xr ssh-keyscan 1 ,
 .Xr chroot 2 ,
+.Xr hosts_access 5 ,
 .Xr login.conf 5 ,
 .Xr moduli 5 ,
 .Xr sshd_config 5 ,
diff --git a/sshd.c b/sshd.c
index 5cd9129d0..d1dd711fc 100644
--- a/sshd.c
+++ b/sshd.c
@@ -129,6 +129,13 @@
 #include <Security/AuthSession.h>
 #endif
 
+#ifdef LIBWRAP
+#include <tcpd.h>
+#include <syslog.h>
+int allow_severity;
+int deny_severity;
+#endif /* LIBWRAP */
+
 #ifndef O_NOCTTY
 #define O_NOCTTY        0
 #endif
@@ -2151,6 +2158,24 @@ main(int ac, char **av)
 #ifdef SSH_AUDIT_EVENTS
         audit_connection_from(remote_ip, remote_port);
 #endif
+#ifdef LIBWRAP
+        allow_severity = options.log_facility|LOG_INFO;
+        deny_severity = options.log_facility|LOG_WARNING;
+        /* Check whether logins are denied from this host. */
+        if (packet_connection_is_on_socket()) {
+                struct request_info req;
+
+                request_init(&req, RQ_DAEMON, __progname, RQ_FILE, sock_in, 0);
+                fromhost(&req);
+
+                if (!hosts_access(&req)) {
+                        debug("Connection refused by tcp wrapper");
+                        refuse(&req);
+                        /* NOTREACHED */
+                        fatal("libwrap refuse returns");
+                }
+        }
+#endif /* LIBWRAP */
 
         /* Log the connection. */
         laddr = get_local_ipaddr(sock_in);