The contents of the /etc/lpd.perm file
is used to specify the restrictions on the use
of the LPRng software,
printers,
and other facilities.
The model used for permission granting is similar to packet filters.
An incoming request is tested against a list of rules,
and the first match found determines the action to be taken.
The action is either ACCEPT or the request is granted,
or REJECT and the request is denied.
You can also establish a default action.
The following is a sample lpd.perms file.
# allow root on server to control jobs
ACCEPT SERVICE=C SERVER REMOTEUSER=root
REJECT SERVICE=C
#
# allow same user on originating host to remove a job
ACCEPT SERVICE=M SAMEHOST SAMEUSER
# allow root on server to remove a job
ACCEPT SERVICE=M SERVER REMOTEUSER=root
REJECT SERVICE=M
# all other operations allowed
DEFAULT ACCEPT
A rule will ACCEPT or REJECT a request if all of the patterns specified in the rule match. If there is a match failure, the next rule in sequence will be applied. If all of the rules are exhausted, then the last specified default authorization will be used.
The sense of a pattern match can be inverted using the NOT keyword.
For example,
the rules with
ACCEPT NOT USER=john,bill
succeeds only if USER is defined and the USER value
is not john or bill.
The following patterns and matching are applied.
|
Keyword | Match |
DEFAULT | default result |
SERVICE | lpC Status and User, lpR, lprM, lpQ request |
USER | user name in print job |
REMOTEUSER | user making request |
HOST | host name in print job |
REMOTEHOST | host making request |
IP | IP address and mask of host in print job |
REMOTEIP | IP address and mask of host making request |
PORT | TCP/IP port of host making request |
SAMEUSER | USER and REMOTEUSER same |
SAMEHOST | HOST and REMOTEHOST same |
SERVER | request originates on lpd server |
FORWARD | destination of job is not host |
GROUP | USER is in the specified group |
LPC | LPC command requested |
REMOTEGROUP | REMOTEUSER is in the specified group |
CONTROLLINE | match a line in control file |
AUTH | authentication type |
AUTHUSER | authenticated user |
AUTHFROM | authenticated forwarder |
AUTHJOB | authenticated job in queue |
Most of the patterns can be lists of alternative values to match,
and can even contain wild cards.
The full details of the rules and keywords are detailed in
the lpd.conf(5) man page.
In order to do matching,
the lpd server obtains and sets up the following information:
getpeername().
The gethostbyaddr() is used to look up the
host's fully qualified domain name,
which is then assigned to the REMOTEHOST value.
The REMOTEIP value is the
set or list of IP addresses that could be
used by this host.
This is possible in the IPV6 environment.gethostbyname() to get the fully qualified domain name of the host.
The IP value is assigned a
set or list of IP addresses that could be
used by this host.When a connection is made to the lpd server,
the originating site's IP address and hostname are determined,
and a check with SERVICE=X is made.
The REMOTEHOST,
REMOTEIP,
and PORT will be defined for the purposes of this check.
If the result is to accept the connection, then the request is then read from the connection, and the SERVICE, REMOTEUSER and PRINTER will be defined. A further check is performed to determine if the service request would be accepted.
When performing a service activity and a particular job is to be acted on, the USER, HOST, and other control file information will be available, and a further check can be performed.
If a rule is specified and the particular value is not defined, then a rule will fail to match.
key=pattern substring match
key=pattern1,pattern2,pattern3,... glob and exact
key=IP1/mask1,IP2/mask2,... IP address
Each of the indicated values is matched against a list of patterns. The following types of matches are used:
[L-H]
specifies a range of characters from
L to H,
in ASCII order.nn.nn.nn.nn format.
The mask must be either an integer number
corresponding to the number of significant bits,
or in the standard nn.nn.nn.nn format.
Addresses are compared by doing
( IPaddr XOR IP ) AND mask
If the result is 0, then a match results. Note that there may be one or more addresses being checked for; this can occur when a host may have multiple IP addresses assigned to it.
low-high,
where low and high are integer numbers.
The match succeeds if the value is in the specified range.
DEFAULT ACCEPT
DEFAULT REJECT
The DEFAULT rule specifies the default if no rule matches. Normally, there is one DEFAULT entry in a permissions file.
Match type: substring
The SERVICE key is based on the type of request.
|
Key | Request |
C | LPC Control Request |
M | LPRM Removal Request |
P | Job Printing |
Q | LPQ Status Request |
R | LPR Job Transfer |
S | LPC Status Request |
X | Connection Request |
Each of the above codes corresponds either directly to the user command, or a set of subcommands.
All the LPC subcommands are SERVICE=C;
status commands such as lpc status, printcap, active,
or lpd are SERVICE=S commands as well.
Match type: GLOB
The USER information is taken from the P (person or logname)
information in the print job control file.
Match type: GLOB
The REMOTEUSER information is taken from the user information sent with a service request.
Note that one of the flaws of RFC1179 is that an LPQ (print status) request does not provide a REMOTEUSER name.
Match type: GLOB
The HOST information is taken from the H (host)
information in the print job control file.
Match type: GLOB
The REMOTEHOST information is obtained by doing a reverse IP name lookup on the remote host address. If there is no FQDN available, then the IP address in text form will be used.
Match type: integer range
The PORT value is obtained from the originating port of the TCP/IP connection. The match succeeds if it is in the specified range.
Match type: IPaddr
The IP information is obtained by doing a DNS lookup on the H (host) information in the control file. If there is no host information, the IP address is undefined. Note that for a single host name there may be multiple IP addresses; address matches are performed against the list of addresses and succeeds if there is one or more individual address matches.
Match type: IPaddr
The REMOTEIP information is the IP address of the host making the
service request.
Note that the REMOTEIP value is obtained by using the
gethostbyaddr lookup to obtain the DNS information for the
remote host. This information may include multiple IP addresses;
address matches are performed against the list of addresses and succeeds
if there is one or more individual address matches.
Match type: GLOB
If you are doing an LPC command, this matches the command. This allows the following permissions line to be used:
#allow remoteuser admin on server to use LPC topq and hold
ACCEPT LPC=topq,hold SERVER REMOTEUSER=x
Match type: exact string match
Both the REMOTEUSER and USER information must be present and identical.
Match type: Same IP Address
The REMOTEHOST and HOST address lists are checked; if there is a common value the match succeeds.
Match type: Same IP Address
One of the REMOTEHOST addresses
must be the same as one of the addresses of the lpd server host,
or must be one of the addresses found by looking up the localhost
name using gethostbyname().
Match type: Address Match
The list of REMOTEHOST and HOST addresses must not have a common entry.
This is identical to NOT SAMEHOST.
This is usually the case when a remote lpd server is forwarding
jobs to the lpd server.
Match type: modified GLOB
If the pattern does not start with a @ character,
then the USER information must be present
and the USER must be present in
one of the groups in /etc/group or whatever permissions mechanism is used
to determine group ownership
which matches the GLOB pattern.
If the pattern starts with a @ character,
then the USER information must be present
and the user must be in the specified netgroup.
This match will be performed only if the netgroup
mechanism is supported on the system and the specified netgroup
exists.
No wildcard match will be done for netgroups.
The same rules as for GROUP, but using the REMOTEUSER value.
Match type: GLOB
A CONTROLLINE pattern has the form
X=pattern1,pattern2,...
X is a single upper case letter. The corresponding line must be present in a control file, and the pattern is applied to the line contents.
This pattern can be used to select only files with specific control file information for printing.
Match type: GLOB
The AUTH value can be NONE, indicating that no authentication was done. If authentication was done, then AUTH=USER checks to see if there was user information, and AUTH=FWD checks to see if there was forwarding system identification.
Match type: GLOB
If AUTH=USER check succeeds, the AUTHUSER rule will check to see if the user identification matches the pattern.
Match type: GLOB
If AUTH=FWD check succeeds, the FWDUSER rule will check to see if the forwarding system identification matches the pattern.
Match type: IPmatch, but for IPV6 as well as IPV4
There is a subtle problem with names and IP addresses which are obtained for 'multi-homed hosts', i.e. - those with multiple ethernet interfaces, and for IPV6 (IP Version 6), in which a host can have multiple addresses, and for the normal host which can have both a short name and a fully qualified domain name.
The IFIP (interface IP) field can be used to check the IP address of the origination of the request, as reported by the information returned by the accept() system call. Note that this information may be IPV4 or IPV6 information, depending on the origination of the system. This information is used by gethostbyaddr() to obtain the originating host fully qualified domain name (FQDN) and set of IP addresses. Note that this FQDN will be for the originating interface, and may not be the cannonical host name. Some systems which use the Domain Name Server (DNS) system may add the cannonical system name as an alias.
Options used:
perms_path= directory path listThe perms_path= configuration variable specifies the
location of the default permissions file.
The default value is:
perms_path=/etc/lpd.perms:/usr/etc/lpd.perms
The lpd.perms file can be obtained by running a program,
in a similar manner to the /etc/printcap file.
See
Filters for details on how
the program would be invoked.
For example, assume the configuration information specified:
perms_path=|/usr/local/libexec/get_perms
Then the get_perms program would be invoked with STDIN attached
to /dev/null and the complete set of permission information
would be read from its STDOUT.
# allow root on server to control jobs
ACCEPT SERVICE=C SERVER REMOTEUSER=root
REJECT SERVICE=C
#
# allow same user on originating host to remove a job
ACCEPT SERVICE=M SAMEHOST SAMEUSER
# allow root on server to remove a job
ACCEPT SERVICE=M SERVER REMOTEUSER=root
REJECT SERVICE=M
# all other operations allowed
DEFAULT ACCEPT
In the above sample, we first specify that
lpC
commands from user root on the lpd server will be accepted.
This is traditionally the way that most lpc commands operate.
Next, we reject any other lpc requests.
We accept
lprM
requests from the host and user that submitted the job,
as well as from root on the server,
and reject any others.
Finally, all other types of commands (lpq, lpr) are allowed by default.
One of the more useful types of permission checking is to restrict access to your printers from users outside your networks. The IP pattern can specify a list of IP addresses and netmasks to apply to them.
For example
IP=10.3.4.0/24 would match all hosts with the IP
addresses
IP=10.3.4.0 to
IP=10.3.4.255.
Similarly, the HOST pattern can specify a set of hostnames or patterns to match against based on the GLOB notation.
For example
REMOTEHOST=*.astart.com
would match all hosts with a DNS entry which ended with
astart.com.
The NOT keyword reverses the match sense. For example
REJECT NOT REMOTEHOST=*.astart.com,*.murpy.com
would reject all requests from hosts which did not have a DNS entry
ending in
astart.com
or
murphy.com.
The following is a more complex lpd.perms file.
# All operations allowed except those specifically forbidden
DEFAULT ACCEPT
#Reject connections which do not originate from hosts with an
# address on 130.191.0.0 or from localhost,
# or name is not assigned to Engineering pc's
REJECT SERVICE=X NOT IFIP=130.191.0.0/16,127.0.0.1/32
REJECT SERVICE=X NOT REMOTEHOST=engpc*
#Do not allow anybody but root or papowell on
#astart1.astart.com or the server to use control
#facilities.
ACCEPT SERVICE=C SERVER REMOTEUSER=root
ACCEPT SERVICE=C REMOTEHOST=astart1.astart.com REMOTEUSER=papowell
#Allow root on talker.astart.com to control printer hpjet
ACCEPT SERVICE=C HOST=talker.astart.com PRINTER=hpjet REMOTEUSER=root
#Reject all others
REJECT SERVICE=C
#Do not allow forwarded jobs or requests
REJECT SERVICE=R,C,M FORWARD
# allow same user on originating host to remove a job
ACCEPT SERVICE=M SAMEHOST SAMEUSER
# allow root on server to remove a job
ACCEPT SERVICE=M SERVER REMOTEUSER=root