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 5fdc696c8..4747ce4a5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1491,6 +1491,62 @@ 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,
@@ -5105,6 +5161,7 @@ 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 41fc5051a..c67846025 100644
--- a/sshd.8
+++ b/sshd.8
@@ -825,6 +825,12 @@ 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 ) .
@@ -929,6 +935,7 @@ 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 0970f2970..72d85de1c 100644
--- a/sshd.c
+++ b/sshd.c
@@ -127,6 +127,13 @@
 #include <Security/AuthSession.h>
 #endif
 
+#ifdef LIBWRAP
+#include <tcpd.h>
+#include <syslog.h>
+int allow_severity;
+int deny_severity;
+#endif /* LIBWRAP */
+
 /* Re-exec fds */
 #define REEXEC_DEVCRYPTO_RESERVED_FD    (STDERR_FILENO + 1)
 #define REEXEC_STARTUP_PIPE_FD          (STDERR_FILENO + 2)
@@ -1978,6 +1985,24 @@ 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);