From f1fe58341ea22a6f07e5e1de79aa0385c0ee0c6a Mon Sep 17 00:00:00 2001 From: Colin Watson Date: Tue, 7 Oct 2014 13:22:41 +0100 Subject: 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 --- configure.ac | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ sshd.8 | 7 +++++++ sshd.c | 25 +++++++++++++++++++++++++ 3 files changed, 89 insertions(+) diff --git a/configure.ac b/configure.ac index 7a25603..128889a 100644 --- a/configure.ac +++ b/configure.ac @@ -1448,6 +1448,62 @@ 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 $LIBS" + AC_MSG_CHECKING([for libwrap]) + AC_LINK_IFELSE([AC_LANG_PROGRAM([[ +#include +#include +#include +#include +int deny_severity = 0, allow_severity = 0; + ]], [[ + hosts_access(0); + ]])], [ + AC_MSG_RESULT([yes]) + AC_DEFINE([LIBWRAP], [1], + [Define if you want + TCP Wrappers support]) + SSHDLIBS="$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, @@ -4953,6 +5009,7 @@ 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 213b5fc..2105979 100644 --- a/sshd.8 +++ b/sshd.8 @@ -850,6 +850,12 @@ 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 ) . @@ -953,6 +959,7 @@ 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 d659a68..9275e0b 100644 --- a/sshd.c +++ b/sshd.c @@ -130,6 +130,13 @@ #include #endif +#ifdef LIBWRAP +#include +#include +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);