in.rshd, rshd - remote shell server
in.rshd [-k5eciU] [-s tos] [-S keytab] [-M realm]
[-L env_var] host.port
in.rshd is the server for the rsh(1) program. The server provides
remote execution facilities with authentication based on Kerberos V5 or
privileged port numbers.
in.rshd is invoked by inetd(8) each time a shell
service is requested.
When Kerberos V5 authentication is required (this can be set with
Kerberos-specific options listed below), the following protocol is
initiated:
- 1.
- Check Kerberos V5 authentication.
- 3.
- A null byte is returned on the initial socket and the command line is
passed to the normal login shell of the user. (The PATH variable is
set to /usr/bin.) The shell inherits the network connections
established by in.rshd.
In order for Kerberos authentication to work, a
host/<FQDN> Kerberos principal must exist for each Fully
Qualified Domain Name associated with the in.rshd server. Each of
these host/<FQDN> principals must have a keytab
entry in the /etc/krb5/krb5.keytab file on the in.rshd server.
An example principal might be:
host/bigmachine.eng.example.com
See kadmin(8) for instructions on adding a principal to a
krb5.keytab file. See for a discussion of Kerberos
authentication.
If Kerberos V5 authentication is not enabled, then in.rshd
executes the following protocol:
- 1.
- The server checks the client's source port. If the port is not in the
range 512-1023, the server aborts the connection. The client's host
address (in hex) and port number (in decimal) are the arguments passed to
in.rshd.
- 2.
- The server reads characters from the socket up to a null (\0) byte.
The resultant string is interpreted as an ASCII number, base
10.
- 3.
- If the number received in step 2 is non-zero, it is interpreted as the
port number of a secondary stream to be used for the stderr. A
second connection is then created to the specified port on the client's
machine. The source port of this second connection is also in the range
512-1023.
- 4.
- A null-terminated user name of at most 16 characters is retrieved on the
initial socket. This user name is interpreted as the user identity on the
client's machine.
- 5.
- A null terminated user name of at most 16 characters is retrieved on the
initial socket. This user name is interpreted as a user identity to use on
the server's machine.
- 6.
- A null terminated command to be passed to a shell is retrieved on the
initial socket. The length of the command is limited by the upper bound on
the size of the system's argument list.
- 7.
- in.rshd then validates the user according to the following steps.
The remote user name is looked up in the password file and a chdir
is performed to the user's home directory. If the lookup fails, the
connection is terminated. If the chdir fails, it does a
chdir to / (root). If the user is not the superuser, (user
ID 0), and if the pam_rhosts_auth PAM module is configured
for authentication, the file /etc/hosts.equiv is consulted for a
list of hosts considered "equivalent". If the client's host name
is present in this file, the authentication is considered successful. See
the SECURITY section below for a discussion of PAM authentication.
If the lookup fails, or the user is the superuser, then the
file .rhosts in the home directory of the remote user is checked
for the machine name and identity of the user on the client's machine.
If this lookup fails, the connection is terminated
- 8.
- A null byte is returned on the initial connection and the command line is
passed to the normal login shell of the user. The PATH variable is
set to /usr/bin. The shell inherits the network connections
established by in.rshd.
The following options are supported:
-5
Same as -k, for backwards compatibility
-c
Requires Kerberos V5 clients to present a cryptographic
checksum of initial connection information like the name of the user that the
client is trying to access in the initial authenticator. This checksum
provides additionl security by preventing an attacker from changing the
initial connection information. This option is mutually exclusive with the
-i option.
-e
Requires the client to encrypt the connection.
-i
Ignores authenticator checksums if provided. This option
ignores authenticator checksums presented by current Kerberos clients to
protect initial connection information. Option -i is the opposite of
option -c.
-k
Allows Kerberos V5 authentication with the
.k5login access control file to be trusted. If this authentication
system is used by the client and the authorization check is passed, then the
user is allowed to log in.
-L env_var
List of environment variables that need to be saved and
passed along.
-M realm
Uses the indicated Kerberos V5 realm. By default, the
daemon will determine its realm from the settings in the
krb5.conf(5)
file.
-s tos
Sets the IP TOS option.
-S keytab
Sets the KRB5 keytab file to use. The
/etc/krb5/krb5.keytab file is used by default.
-U
rshd and in.rshd are IPv6-enabled. See ip6(4P). IPv6
is not currently supported with Kerberos V5 authentication.
The Kerberized rshd service runs on port 544 (kshell). The
corresponding FMRI entry is: :
svc:/network/shell:kshell (rshd with kerberos (ipv4 only))
in.rshd uses pam(3PAM) for authentication, account management, and
session management. The PAM configuration policy, listed through
/etc/pam.conf, specifies the modules to be used for in.rshd.
Here is a partial pam.conf file with entries for the rsh command
using rhosts authentication, UNIX account management, and session
management module.
| rsh |
auth |
required |
pam_rhosts_auth.so.1 |
| rsh |
account |
required |
pam_unix_roles.so.1 |
| rsh |
session |
required |
pam_unix_projects.so.1 |
| rsh |
session |
required |
pam_unix_account.so.1 |
| rsh |
session |
required |
pam_unix_session.so.1 |
If there are no entries for the rsh service, then the
entries for the "other" service are used. To maintain the
authentication requirement for in.rshd, the rsh entry must always be
configured with the pam_rhosts_auth.so.1 module.
in.rshd can authenticate using Kerberos V5 authentication
or pam(3PAM). For Kerberized rsh service, the appropriate
PAM service name is krsh.
/etc/hosts.equiv
$HOME/.k5login
File containing Kerberos principals that are allowed
access.
/etc/krb5/krb5.conf
Kerberos configuration file.
rsh(1), svcs(1), pam(3PAM), getnameinfo(3SOCKET),
ip6(4P), hosts(5), krb5.conf(5), pam.conf(5),
attributes(7), environ(7), krb5_auth_rules(7),
pam_authtok_check(7), pam_authtok_get(7),
pam_authtok_store(7), pam_dhkeys(7), pam_passwd_auth(7),
pam_rhosts_auth(7), pam_unix_account(7),
pam_unix_auth(7), pam_unix_session(7), smf(7),
inetadm(8), inetd(8), kadmin(8), svcadm(8)
The following diagnostic messages are returned on the connection associated with
stderr, after which any network connections are closed. An error is
indicated by a leading byte with a value of 1 in step 8 above (0 is
returned above upon successful completion of all the steps prior to the
command execution).
locuser too long
The name of the user on the client's machine is longer
than 16 characters.
remuser too long
The name of the user on the remote machine is longer than
16 characters.
command too long
The command line passed exceeds the size of the argument
list (as configured into the system).
Hostname for your address unknown.
No entry in the host name database existed for the
client's machine.
Login incorrect.
No password file entry for the user name existed.
Permission denied.
The authentication procedure described above
failed.
Can't make pipe.
The pipe needed for the stderr was not
created.
Try again.
A fork by the server failed.
The authentication procedure used here assumes the integrity of each client
machine and the connecting medium. This is insecure, but it is useful in an
"open" environment.
A facility to allow all data exchanges to be encrypted should be
present.
The pam_unix(7) module is no longer supported. Similar
functionality is provided by pam_authtok_check(7),
pam_authtok_get(7), pam_authtok_store(7),
pam_dhkeys(7), pam_passwd_auth(7), pam_unix_account(7),
pam_unix_auth(7), and pam_unix_session(7).
The in.rshd service is managed by the service management
facility, smf(7), under the service identifier:
svc:/network/shell:default
Administrative actions on this service, such as enabling,
disabling, or requesting restart, can be performed using svcadm(8).
Responsibility for initiating and restarting this service is delegated to
inetd(8). Use inetadm(8) to make configuration changes and to
view configuration information for this service. The service's status can be
queried using the svcs(1) command.