path: root/src/share/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

# 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=$(gpg_user --list-key --fixed-list-mode --with-colon \
    --with-fingerprint --with-fingerprint \
    ="$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
}


# the ssh proxycommand function itself
ssh_proxycommand() {
local hostKey

if [ "$1" = '--no-connect' ] ; then
    NO_CONNECT='true'
    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}"

# 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)
        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}

# update the known_hosts file for the host
local returnCode=0
source "${MSHAREDIR}/update_known_hosts"
update_known_hosts "$HOSTP" || returnCode="$?"

# output on depending on the return of the update-known_hosts
# subcommand, which is (ultimately) the return code of the
# update_known_hosts function in common
case "$returnCode" in
    0)
    # acceptable host key found so continue to ssh
    true
    ;;
    1)
    # no hosts at all found so also continue (drop through to
    # regular ssh host verification)
    true
    ;;
    2)
    # at least one *bad* host key (and no good host keys) was
    # found, so output some usefull information
    output_no_valid_key
    ;;
    *)
    # anything else drop through
    true
    ;;
esac

# 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?

# exec a netcat passthrough to host for the ssh connection
if [ -z "$NO_CONNECT" ] ; then
    if (type nc &>/dev/null); then
    exec nc "$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

}