The file lpd.perms is used to provide permission information for
the LPRng Printer spooler system.
Blank lines and all
characters after a hash sign (#) to the end of line are ignored.
If a hash sign is desired in the
it should be escaped with a backslash
All other lines
specify permissions entry and should be of the following form:
ACCEPT [[not] key = value[,value]* ]*
REJECT [[not] key = value[,value]* ]*
Each LPD service request is checked against
the entries in the permissions database or file.
The following is a typical permissions file:
# Set default permissions
# Reject any connections from outside our subnet
REJECT SERVICE=X NOT REMOTEIP=22.214.171.124/255.255.0.0
# Only accept spooling (LPR) from
# Engineering Lab or the Deans office
REJECT SERVICE=R NOT REMOTEHOST=*.eng.sdsu.edu,dean.sdsu.edu
# Do not accept forwarded jobs for printing
REJECT SERVICE=R FORWARD
# Allow only the administrators control access
ACCEPT SERVICE=C,M REMOTEHOST=spooler.eng.sdsu.edu REMOTEUSER=root,papowell
ACCEPT SERVICE=C,M SERVER REMOTEUSER=root,papowell
# Allow only the user on the same host who spooled job to remove it
ACCEPT SERVICE=M SAMEUSER SAMEHOST
# Allow users to check status
ACCEPT SERVICE=C LPC=status
# Require connection for other operations over UNIX socket
# not TCP/IP port. Effectively requiring them to be made from the
ACCEPT SERVICE=C UNIXSOCKET
# Variation - accept all spooled jobs, but then apply
# permissions checking when job is printed. Allows
# prevents remote spoolers from locking up trying resend
# same request
REJECT SERVICE=P NOT REMOTEHOST=*.eng.sdsu.edu,dean.sdsu.edu
Permission checking is done by using a set of keys (or fields)
with associated values to check for permission.
The SERVICE key has value P for printing (i.e.- unspooling),
R for spooling (i.e.- LPR request),
P for printing (i.e., after job has been spooled),
C printer control (i.e. - LPC),
M for removal (i.e.- LPRM request),
Q for queue information (i.e.- LPQ request).
X key is used when checking for connection information.
all of the keys have undefined or NULL values,
and are assigned values during the permissions checking process.
When a connection is made to the server,
The REMOTEHOST (alias REMOTEIP) key the list of IP addresses and hostnames
determined by doing a reverse Domain Name Service (DNS)
lookup on the remote hosts IP address.
If the reverse DNS fails,
then only the IP address will be used.
The REMOTEPORT (PORT is an alias for REMOTEPORT) is assigned
the port number of the connection origination.
The UNIXSOCKET key will match (be true) if the connection
is over a UNIX socket.
this is from the localhost.
the SERVICE value is assigned X,
and the lpd server will check the database to see if the
connection is accepted or rejected.
The server will then read the request information from the connection.
If the request is for an authenticated data transfer,
the server will invoke the appropriate authentication mechanism
which will assign AUTH a true (or matching) value,
AUTHTYPE the type of authentication,
AUTHUSER the authenticated user id value, which may differ from the
actual user name,
and AUTHFROM the authenticated identification of the originator
of the request,
which may be a server if the request is forwarded.
the SERVICE value is set to R, C, M, or Q depending on whether it is
an LPR, LPC, LPRM, or LPQ request,
and the LPC value set to the requested LPC command if it was an LPC
If the request contained a user name,
then REMOTEUSER is set to this name.
If the request contained a printer name,
then PRINTER is set to the printer name.
If the request is a print request,
then the HOST value is set to the list of host names and IP
addresses given by a DNS lookup of the value in the
H field of the job.
The database is scanned again to determine if the operation can be
performed on the requested queue.
To simplify the rule writing,
if the operation requires modification or checking of individual
such as the LPC, LPQ, or LPRM commands,
then the various checks that depend on jobs will succeed in this step.
if the operation requires modification or checking of individual
such as the LPC, LPQ, or LPRM commands,
then the specified print queue is scanned,
and for each job in the print queue,
the HOST and USER values are set to the host and user
values in the control file for the job.
The database is checked as follows.
Each line of the permissions file is scanned for key names and
values, and these are matched against the request keys information.
When all matches on a line are made,
then search terminates with the specified action (ACCEPT/REJECT).
If no match is found the default permission value is used.
DEFAULT key is used to specify the current default permission to
be used for successful matches or if there is no match after
scanning the entire permissions database.
The following keys provide some additional checking capabilities.
The REMOTEGROUP entry checks that the REMOTEUSER
value appears in a group or netgroup entry in the system database,
and the GROUP entry for the USER value.
would check to see if any of the group names matching
student* or staff* have the specified user name in them.
If a system has the
a printer, group, or remotegroup name starting with a
will be treated as a netgroup name,
and specified user name or printer will be checked to see if
it is in the group.
The SERVER entry will be true (match) if the request originated from
the print server.
The SAMEHOST is true (matches) if the REMOTEHOST and HOST values
have a common entry,
i.e. - are the same host.
The SAMEUSER is true (matches) if the REMOTEUSER and USER values are identical.
The AUTHSAMEUSER is true (matches) if the AUTHUSER
value that originated the request and the AUTHUSER which
was used to transfer a job are identical.
AUTHJOB is true (matches) if the job was transferred using authentication.
The FORWARD value is an alias for NOT SAMEHOST.
The CONTROLLINE value can be used to determine if there is a matching line
in the control file.
This facility has been used to ensure that jobs contain various
information fields in order to be printed.
Key Match Connect Job Job LPQ LPRM LPC
SERVICE S X R P Q M C,S
USER S - JUSR JUSR JUSR JUSR JUSR
HOST S RH JH JH JH JH JH
GROUP S - JUSR JUSR JUSR JUSR JUSR
REMOTEPORT N PORT PORT - PORT PORT PORT
REMOTEUSER S - JUSR JUSR JUSR CUSR CUSR
REMOTEHOST S RH RH JH RH RH RH
UNIXSOCKET V SK SK SK SK SK SK
REMOTEGROUP S - JUSR JUSR JUSR CUSR CUSR
CONTROLLINE S - CL CL CL CL CL
PRINTER S - PR PR PR PR PR
FORWARD V - SA - - SA SA
SAMEHOST V - SA - SA SA SA
SAMEUSER V - - - SU SU SU
SERVER V - SV - SV SV SV
AUTH V - AU - AU AU AU
AUTHTYPE S - AU - AU AU AU
AUTHUSER S - AU - AU AU AU
AUTHSAMEUSER S - AU - AU AU AU
AUTHFROM S - AU - AU AU AU
AUTHJOB V - AU - AU AU AU
PORT is alias for REMOTEPORT
REMOTEIP is alias for REMOTEHOST
IP is alias for HOST
JH = HOST host in control file
RH = REMOTEHOST connecting host name/IP
JUSR = USER user in control file
CUSR = REMOTEUSERuser from control request
JIP= IP host/IP addr of host in control file
RIP= REMOTEIP host/IP addr of requesting host
PORT= connecting host origination port
SK= match if connection over a UNIX socket
CONTROLLINE= pattern match of control line in control file
FW= IP of source of request == IP of host in control file
SA= IP of source of request == IP of host in control file
SU= user from request == user in control file
SA= IP of source of request == IP of server host
SV= matches if from same address as server
AU= value determined by server authentication operation
AUTH is true if authenticated transfer,
TYPE is set to the type of authentication (kerberos, etc)
AUTHUSER is user authentication id
AUTHFROM is sender authentication id (can be remote server)
AUTHSAMEUSER matches if remote user authentication id matches original
user authentication id
AUTHJOB it true if print job has authentication
Match: S = string with wild card, IP = IP address[/netmask],
N = low[-high] number range, V = exact value match
SERVICE: X - Connection request; R - lpr request from remote host;
P - print job in queue; Q - lpq request, M - lprm request;
C - lpc spool control request; S - lpc spool status request
U - administratively allowed user operation
NOTE: when printing (P action), the remote and job check values
(i.e. - RUSR, JUSR) are identical.
The special key
letter=patterns searches the control file line starting with the
(upper case) letter,
and is usually used with printing and spooling checks.
would check that the class information (i.e.- line in the control file
starting with C) had a value starting with A or B.
A permission line consists of a list of tests and a result value.
If all of the tests succeed, then a match has been found and the
permission testing completes with the result value. You use the
DEFAULT reserved word to set the default ACCEPT/DENY result.
The NOT keyword will reverse the sense of a test.
Each test can have one or more optional values separated by
commas. For example USER=john,paul,mark has 3 test values.
The Match value specifies how the matching is done.
S = string type match - string match with glob.
Format: string with wildcards (*)
* matches 0 or more chars
Character comparison is case insensitive.
For example - USER=th*s matches uTHS, This, This, Theses
IP = IP address and submask. IP address must be in dotted form.
Format: x.x.x.x[/y.y.y.y or /z]
x.x.x.x is IP address
y.y.y.y is optional submask, default is 255.255.255.255
z is a netmask with most significant z bits set.
Match is done by IP address to a 32 bit value and using:
success = ((x ^ IP ) & y) == 0 (C language notation)
i.e.- only bits where mask is non-zero are used in comparison.
For example - IP=126.96.36.199/255.255.0.0 matches all address 130.191.X.X
IP=188.8.131.52/16 has the same value.
N = numerical range - low-high integer range.
Example: PORT=0-1023 matches a port in range 0 - 1023 (privileged)
The authentication entries
AUTHUSER, AUTHSAMEUSER and AUTHFROM
can be used to check permissions for authenticated operations.
AUTH is set (true) if authentication was done.
We can use this to reject non-authenticated transfers:
REJECT NOT AUTH
The AUTHTYPE will match the authentication type
being used or requested by the remote client or server.
The AUTHUSER matches the original client authentication information
used by the client to make a request to the server,
and the AUTHFROM matches the sender authentication information.
The AUTHSAMEUSER will match if the remote client or user authentication
id is the same as that used for the job generation.