NAME
innbind - Helper program to bind sockets to privileged ports
SYNOPSIS
innbind [-p] fd,family,address,port [...]
DESCRIPTION
innbind is a helper program that’s not meant to be run directly.
Instead, innd and nnrpd use it internally to bind to ports that require
root privileges to bind to.
This program must be installed setuid root in order for innd or nnrpd
to bind to ports under 1024. The only functions that it’s willing to
perform are to bind an open file descriptor to a given address and port
or to create a new socket, bind it, and return the bound socket to its
caller. It can only be run as the news user (as specified at configure
time), and will only bind to ports 119, 433, 563, an additional port
specified with the --with-innd-port argument to configure, or ports
numbered 1024 or higher.
Each argument to innbind must be a comma-separated list of four
elements. The first is the file descriptor number that should be
bound, the second is the numeric family of the socket (AF_INET or
AF_INET6), the third is the local address to bind to (in dotted-quad
format for IPv4 and in colon-separated address format for IPv6), and
the fourth is the port number. To bind to all addresses with IPv4, use
0.0.0.0 as the address. To bind to all addresses with IPv6, use "::"
as the address.
Multiple arguments can be specified to tell innbind to bind multiple
sockets at the same time. Any errors (other than permission denied
-- see below) encountered will cause innbind to abort, and error
messages will be sent both to syslog and to standard error.
By default, innbind attempts to just bind the already open file
descriptor that it inherits from its caller. For each successfully
bound file descriptor (in the order given on the command line), innbind
prints "ok" and a newline to its standard output.
On some systems (apparently just STREAMS-based systems), however, even
a setuid root program cannot bind a socket to a privileged port that
was created by a process that didn’t have permissions. If innbind gets
permission denied when trying to bind a socket, it will print "no" and
a newline to its standard output. It will then create a new socket,
bind it as specified, and then attempt to pass that socket back to its
caller using the I_SENDFD STREAMS ioctl. The caller should receive
that file descriptor with I_RECVFD and use it instead of the one that
it created.
Note that file descriptor passing is only supported on STREAMS-based
systems since it is done with ioctls over a pipe. However, it is
believed that those systems are exactly the systems that can’t simply
bind the inherited file descriptor. If this assumption proves to be
incorrect, traditional BSD file descriptor passing over a Unix domain
socket will have to be added.
OPTIONS
-p If given as the first command-line argument, no attempt will be
made to bind the inherited file descriptor and innbind will only
try creation of a new file descriptor and passing it back via
standard output. This option is primarily useful for testing.
SECURITY
As innbind is normally installed setuid root, security is even more of
an issue for it than for other parts of INN. It is a fairly short
program, and if you understand C, you are encouraged to audit it
yourself to be certain that it does only what it is supposed to do.
The only INN library functions it uses are the vector functions, the
message functions for error reporting, and xstrdup.
The ports that will be bound are restricted to prevent potential
attacks made possible by the ability to bind low-numbered ports, such
as exploits of the rsh(1) family of commands on some systems. If
innbind is installed setuid root, it can only be executed by the news
user to prevent other users on the system from being able to bind to
even those few privileged ports that it allows.
innbind uses no external configuration files; the only files it might
open are through the system getpwnam(3) service to get the UID of the
news user. The only user input that it accepts are its command-line
arguments.
DIAGNOSTICS
innbind may log the following messages to syslog and print them to
standard error.
cannot create socket for %s: %s
(Fatal) innbind fell back on attempting to create a new socket to
bind for the given argument, and the socket creation failed.
cannot bind socket for %s: %s
(Fatal) Calling bind for the socket corresponding to the given
argument failed with a system error. If the error indicates
permission denied, make sure that innbind is setuid root. This can
also be caused by trying to use IPv6 on a system whose kernel does
not support it.
cannot bind to restricted port %hu in %s
(Fatal) The port number portion of the given command-line argument
is for a port below 1024 which is not 119, 433, 563, or a port
given to --with-innd-port at configure time. Other ports are not
allowed for security reasons.
cannot get socket options for file descriptor %d: %s
(Fatal) innbind was unable to get the socket options for that file
descriptor. The most likely cause of this error is passing the
wrong file descriptor number to innbind (a file descriptor that
isn’t open, or that corresponds to a regular file rather than a
network socket).
cannot get UID for %s
(Fatal) innbind was unable to get the UID for the news user
specified during configure (and defaulting to "news"). This
normally means that user isn’t in the system passwd file.
cannot mark socket reusable for %s: %s
(Fatal) innbind created a new socket for the given argument but was
unable to mark its bind address reusable (the SO_REUSEADDR socket
option).
cannot pass file descriptor: %s
(Fatal) innbind created and bound a new file descriptor but was
unable to pass it back to its caller via its standard output, using
the I_SENDFD STREAMS ioctl.
invalid file descriptor %d: not SOCK_STREAM
(Fatal) The given file descriptor is not a SOCK_STREAM socket.
innbind can only bind SOCK_STREAM sockets.
invalid IPv4 address %s in %s
(Fatal) The IPv4 address specified in the given command-line option
could not be parsed by inet_aton(3). IPv4 addresses should be
specified in the standard dotted-quad format (10.2.3.4).
invalid IPv6 address %s in %s
(Fatal) The IPv6 address specified in the given command-line option
could not be parsed by inet_pton(3). IPv6 addresses should be
specified in RFC 4291 format (1080:0:0:0:8:800:200C:417A or
1080::8:800:200C:417A).
invalid command-line argument %s
(Fatal) The specified command-line argument could not be parsed or
was not in the correct format.
invalid file descriptor %s in %s
(Fatal) The file descriptor portion of the given command-line
argument is not a non-negative integer.
invalid port number %s in %s
(Fatal) The port number portion of the given command-line argument
is not a non-negative integer.
invalid protocol family %s in %s
(Fatal) The protocol family portion of the given command-line
argument is not a non-negative integer. It should be equal to
either AF_INET or AF_INET6 on the system where innbind is run.
must be run by user %s (%lu), not %lu
(Fatal) When setuid root, innbind may only be run by the news user
as specified at configure time ("news" by default), for security
reasons.
no addresses specified
(Fatal) No arguments were given on the command line (except maybe
-p).
port may not be zero in %s
(Fatal) The port number portion of the given command-line argument
was zero.
unknown protocol family %s in %s
(Fatal) The protocol number portion of the given command-line
argument is neither AF_INET nor AF_INET6.
EXAMPLES
As mentioned above, innbind is never run directly, only by innd and
other programs that need to bind to and listen to network ports.
Sample invocations by innd would be:
innbind 3,10,::,119
to bind the IPv6 socket on file descriptor 3 to port 119, all
addresses, or:
innbind 6,2,10.0.0.3,433
to bind the IPv4 socket on file descriptor 6 to port 433 in the address
10.0.0.3.
HISTORY
Written by Russ Allbery <rra@stanford.edu> for InterNetNews.
$Id: innbind.pod 8894 2010-01-17 13:04:04Z iulius $
SEE ALSO
inet_aton(3), inet_pton(3), innd(8), nnrpd(8).