monkeysphere 0.37-2 / usr / share / monkeysphere / m / ssh_proxycommand

# -*-shell-script-*-
# This should be sourced by bash (though we welcome changes to make it POSIX sh compliant)

# Monkeysphere ssh-proxycommand subcommand
#
# The monkeysphere scripts are written by:
# Jameson Rollins <jrollins@finestructure.net>
# Daniel Kahn Gillmor <dkg@fifthhorseman.net>
#
# They are Copyright 2008-2009, and are all released under the GPL,
# version 3 or later.

# This is meant to be run as an ssh ProxyCommand to initiate a
# monkeysphere known_hosts update before an ssh connection to host is
# established.  Can be added to ~/.ssh/config as follows:
#  ProxyCommand monkeysphere ssh-proxycommand %h %p

# the ssh proxycommand function itself
ssh_proxycommand() {
    local connect='true'
    local HOST
    local PORT
    local HOSTP
    local URI

    if [[ "$1" == '--no-connect' ]] ; then
	connect='false'
	shift 1
    fi

    HOST="$1"
    PORT="$2"

    if [ -z "$HOST" ] ; then
	log error "Host not specified."
	usage
	exit 255
    fi
    if [ -z "$PORT" ] ; then
	PORT=22
    fi

    # set the host URI
    if [ "$PORT" != '22' ] ; then
	HOSTP="${HOST}:${PORT}"
    else
	HOSTP="${HOST}"
    fi
    URI="ssh://${HOSTP}"

    # passed HOST/PORT/HOSTP/URI
    validate_monkeysphere

    # exec a netcat passthrough to host for the ssh connection
    if [[ "$connect" == 'true' ]] ; then
	if (type nc &>/dev/null); then
	    exec nc "$HOST" "$PORT"
	elif (type socat &>/dev/null); then
	    exec socat STDIO "TCP:$HOST:$PORT"
	else
	    echo "Neither netcat nor socat found -- could not complete monkeysphere-ssh-proxycommand connection to $HOST:$PORT" >&2
	    exit 255
	fi
    fi
}

validate_monkeysphere() {
    local hostKey

    # specify keyserver checking.  the behavior of this proxy command
    # is intentionally different than that of running monkeyesphere
    # normally, and keyserver checking is intentionally done under
    # certain circumstances.  This can be overridden by setting the
    # MONKEYSPHERE_CHECK_KEYSERVER environment variable, or by setting
    # the CHECK_KEYSERVER variable in the monkeysphere.conf file.

    # if the host is in the gpg keyring...
    if gpg_user --list-key ="${URI}" &>/dev/null ; then
	# do not check the keyserver
	CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"}

    # if the host is NOT in the keyring...
    else
	# FIXME: what about system-wide known_hosts file (/etc/ssh/known_hosts)?

	if [ -r "$KNOWN_HOSTS" ]; then
	    # look up the host key is found in the known_hosts file...
            if (type ssh-keygen &>/dev/null) ; then
		hostKey=$(ssh-keygen -F "$HOST" -f "$KNOWN_HOSTS" 2>/dev/null || true)
            else
		# FIXME: we're not dealing with digested known_hosts
		# if we don't have ssh-keygen

		# But we could do this without needing ssh-keygen.
		# hashed known_hosts looks like: |1|X|Y where 1 means
		# SHA1 (nothing else is defined in openssh sources), X
		# is the salt (same length as the digest output),
		# base64-encoded, and Y is the digested hostname (also
		# base64-encoded).

		# see hostfile.{c,h} in openssh sources.

		hostKey=$(cut -f1 -d\  < .ssh/known_hosts | tr ',' '\n' | grep -Fx -e "$HOST" || :)
            fi
	fi

	if [ "$hostKey" ] ; then
	# do not check the keyserver
	# FIXME: more nuanced checking should be done here to properly
	# take into consideration hosts that join monkeysphere by
	# converting an existing and known ssh key
	    CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"}

	# if the host key is not found in the known_hosts file...
	else
	    # check the keyserver
	    CHECK_KEYSERVER=${CHECK_KEYSERVER:="true"}
	fi
    fi

    # finally look in the MONKEYSPHERE_ environment variable for a
    # CHECK_KEYSERVER setting to override all else
    CHECK_KEYSERVER=${MONKEYSPHERE_CHECK_KEYSERVER:=$CHECK_KEYSERVER}

    declare -i KEYS_PROCESSED=0
    declare -i KEYS_VALID=0

    # update the known_hosts file for the host
    source "${MSHAREDIR}/update_known_hosts"
    update_known_hosts "$HOSTP"

    if ((KEYS_PROCESSED > 0)) && ((KEYS_VALID == 0)) ; then
	log debug "output ssh marginal ui..."
	output_no_valid_key
    fi

    # FIXME: what about the case where monkeysphere successfully finds
    # a valid key for the host and adds it to the known_hosts file,
    # but a different non-monkeysphere key for the host already exists
    # in the known_hosts, and it is this non-ms key that is offered by
    # the host?  monkeysphere will succeed, and the ssh connection
    # will succeed, and the user will be left with the impression that
    # they are dealing with a OpenPGP/PKI host key when in fact they
    # are not.  should we use ssh-keyscan to compare the keys first?
}

# output the key info, including the RSA fingerprint
show_key_info() {
    local keyid="$1"
    local sshKeyGPGFile
    local sshFingerprint
    local gpgSigOut
    local otherUids

    # get the ssh key of the gpg key
    sshFingerprint=$(gpg2ssh "$keyid" | "$SYSSHAREDIR/keytrans" sshfpr)

    # get the sigs for the matching key
    gpgSigOut=$(gpg_user --check-sigs \
        --list-options show-uid-validity \
        "$keyid")

    echo | log info

    # output the sigs, but only those on the user ID
    # we are looking for
    echo "$gpgSigOut" | awk '
{
if (match($0,"^pub")) { print; }
if (match($0,"^uid")) { ok=0; }
if (match($0,"^uid.*'$userID'$")) { ok=1; print; }
if (ok) { if (match($0,"^sig")) { print; } }
}
'

    # output ssh fingerprint
    cat <<EOF
RSA key fingerprint is ${sshFingerprint}.
EOF

    # output the other user IDs for reference
    otherUids=$(echo "$gpgSigOut" | grep "^uid" | grep -v "$userID")
    if [ "$otherUids" ] ; then
	log info <<EOF

Other user IDs on this key:
EOF
	echo "$otherUids" | log info
    fi

}

# "marginal case" ouput in the case that there is not a full
# validation path to the host
output_no_valid_key() {
    local userID
    local sshKeyOffered
    local gpgOut
    local type
    local validity
    local keyid
    local uidfpr
    local usage
    local sshKeyGPG
    local tmpkey
    local returnCode=0

    userID="ssh://${HOSTP}"

    LOG_PREFIX=

    # if we don't have ssh-keyscan, we just don't scan:
    if ( type ssh-keyscan &>/dev/null ) ; then
    # retrieve the ssh key being offered by the host
        sshKeyOffered=$(ssh-keyscan -t rsa -p "$PORT" "$HOST" 2>/dev/null \
	    | awk '{ print $2, $3 }')
    fi

    # get the gpg info for userid
    gpgOut=$(gpg_user --list-key --with-colons \
	--with-fingerprint --with-fingerprint \
	="$userID" 2>/dev/null)

    # output header
    log info <<EOF
-------------------- Monkeysphere warning -------------------
Monkeysphere found OpenPGP keys for this hostname, but none had full validity.
EOF

    # output message if host key could not be retrieved from the host
    if [ -z "$sshKeyOffered" ] ; then
	log info <<EOF
Could not retrieve RSA host key from $HOST.
EOF
	# check that there are any marginally valid keys
	if echo "$gpgOut" | egrep -q '^(pub|sub):(m|f|u):' ; then
	    log info <<EOF
The following keys were found with marginal validity:
EOF
	fi
    fi

    # find all keys in the gpg output ('pub' and 'sub' lines) and
    # output the ones that match the host key or that have marginal
    # validity
    echo "$gpgOut" | cut -d: -f1,2,5,10,12 | \
    while IFS=: read -r type validity keyid uidfpr usage ; do
	case $type in
	    'pub'|'sub')
		# get the ssh key of the gpg key
		sshKeyGPG=$(gpg2ssh "$keyid")
		# if a key was retrieved from the host...
		if [ "$sshKeyOffered" ] ; then
		    # if one of the keys matches the one offered by
		    # the host, then output info and return
		    if [ "$sshKeyGPG" = "$sshKeyOffered" ] ; then
			log info <<EOF
An OpenPGP key matching the ssh key offered by the host was found:
EOF
			show_key_info "$keyid" | log info
			# this whole process is in a "while read"
			# subshell.  the only way to get information
			# out of the subshell is to change the return
			# code.  therefore we return 1 here to
			# indicate that a matching gpg key was found
			# for the ssh key offered by the host
			return 1
		    fi
		# else if a key was not retrieved from the host...
		else
		    # and the current key is marginal, show info
		    if [ "$validity" = 'm' ] \
			|| [ "$validity" = 'f' ] \
			|| [ "$validity" = 'u' ] ; then
			show_key_info "$keyid" | log info
		    fi
		fi
		;;
	esac
    done || returnCode="$?"

    # if no key match was made (and the "while read" subshell
    # returned 1) output how many keys were found
    if (( returnCode == 1 )) ; then
	echo | log info
    else
	# if a key was retrieved, but didn't match, note this
	if [ "$sshKeyOffered" ] ; then
	    log info <<EOF
None of the found keys matched the key offered by the host.
EOF
	fi

	# note how many invalid keys were found
	nInvalidKeys=$(echo "$gpgOut" | egrep '^(pub|sub):[^(m|f|u)]:' | wc -l)
	if ((nInvalidKeys > 0)) ; then
	    log info <<EOF
Keys found with less than marginal validity: $nInvalidKeys
EOF
	fi

	log info <<EOF
Run the following command for more info about the found keys:
gpg --check-sigs --list-options show-uid-validity =${userID}
EOF

	# FIXME: should we do anything extra here if the retrieved
	# host key is actually in the known_hosts file and the ssh
	# connection will succeed?  Should the user be warned?
	# prompted?
    fi

    # output footer
    log info <<EOF
-------------------- ssh continues below --------------------
EOF
}