Write man pages and do some misc cleanup on old files.

Add more documentation to the README.
This commit is contained in:
Nicholas J. Kain 2011-07-13 02:30:10 -04:00
parent 2a1885bab4
commit 24db573005
8 changed files with 260 additions and 505 deletions

85
README
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@ -1,14 +1,12 @@
ndhc + ifchd, copyright (c) 2004-2011 Nicholas Kain. Licensed under GNU GPL2.
ndhc + ifchd, Copyright (C) 2004-2011 Nicholas J. Kain.
Licensed under GNU GPL v2.
Requirements:
Linux kernel (tested: 2.4, 2.6)
* libcap is required (available via ftp.kernel.org)
C99-compliant C compiler (for C99 struct subobject init)
* any modern GCC should be sufficient
CMake (tested: 2.8)
Linux kernel (2.4 used to work long ago, but I only test 2.6 now)
C99-compliant C compiler (any recent GCC will work)
GNU Make (tested: 3.82) or CMake (tested: 2.8)
libcap (available via ftp.kernel.org)
Tested with glibc. dietlibc is not compatible. I have not tested uclibc.
@ -51,6 +49,42 @@ explicitly deconfigured. This functionality can be useful on wired networks
when transient carrier downtimes occur (or cables are changed), but it is
particularly useful on wireless networks.
FEATURES
--------
Privilege-seperated. Neither ifchd or ndhc runs as full root, and capabilities
are divided between the programs. Both programs run in a chroot.
Robust. ndhc performs no runtime heap allocations -- malloc() is never called
(and neither is brk(), mmap(), etc), and ndhc never performs recursive calls
and only stack-allocates fixed-length types, so stack depth is bounded, too.
ifchd lightly uses malloc(), but no heap allocations have long lifetimes, and
are bounded from being large.
Active defense of IP address and IP collision avoidance. ndhc fully implements
RFC5227. It is capable of both a normal level of tenacity in defense, where
it will eventually back off and request a new lease if a peer won't relent
in the case of a conflict, and of relentlessly defending a lease forever. In
either mode, it rate-limits defense messages, so it can't be tricked into
flooding by a hostile peer or DHCP server, either.
Small. Both ndhc and ifchd avoid outside dependencies and are written in
plain C.
Fast. ndhc filters input using the BPF/LPF mechanism so that uninteresting
packets are dropped by the operating system before ndhc even sees the data.
ndhc also only listens to DHCP traffic when it's necessary.
Flexible. ndhc can request particular IPs, send user-specified client IDs,
write a file that contains the current lease IP, write PID files, etc. One
ifchd session can service multiple ndhc sessions.
Aware of the hardware link status. If you disconnect an interface on which
ndhc is providing dhcp service, it will be aware. When the link status
returns, ndhc will fingerprint the reconnected network and make sure that it
corresponds to the one on which it has a lease. If the new network is
different, it will forget about the old lease and request a new one.
USAGE
-----
@ -153,8 +187,10 @@ be used multiple times to allow multiple interfaces.
PORTING NOTES
-------------
ndhc is rather platform-dependent, and it extensively uses Linux-specific
features. Some of these features are also available on the BSDs.
DHCP clients aren't naturally very portable. It's necessary to perform a lot
of tasks that are platform-specific. ndhc is rather platform-dependent, and it
extensively uses Linux-specific features. Some of these features are also
available on the BSDs.
1) Both ndhc and ifchd use the SO_PEERCRED flag of getsockopt() to discriminate
authorized connections by uid, gid, and pid. Similar functionality exists in
@ -265,5 +301,34 @@ Make sure that CONFIG_GRKERNSEC_CHROOT_CAPS is disabled. Otherwise, ifchd will
lose its capabilities (in particular, the ability to reconfigure interfaces)
when it chroots.
DHCP PROTOCOL QUIRKS
--------------------
Send a packet that has an options field set to:
'DHCP-OPTION-OVERLOAD:3'
Then in the file and sname fields:
'DHCP-OPTION-OVERLOAD:3'
I suspect some bad dhcp programs will hang given this input.
Options concatenation is a minefield of poor specification. There's a
follow-up RFC to make proper behavior somewhat more defined, but it's still
overly complex.
DHCP explicitly specifies that there is no minimum lease time and also
specifies that the minimum default rebinding time is leasetime*0.875 and
the minimum default renewing time is leasetime*0.500. All times are relative
to the instant when the lease is bound and are specified in seconds. Taken
together, this means that a client strictly implementing the RFC should
accept a lease that either is perpetually rebinding (lease == 1s) or instantly
expires (lease == 0s). ndhc ignores the RFC and specifies a minimum lease
time of one minute.
Renew and rebind times are optionally specified and may take on any value.
This means that a malicious server could demand a rebind time before a renew
time, or make these times ridiculously short, or specify both times past
that of the lease duration. ndhc avoids all of this nonsense by simply
ignoring these options and using the default values specified by the RFC.
There are other quirks, but these are just several interesting ones that
immediately occur to me while I'm writing this document.

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20040906
accept_conns() trivial correctness fix: EINTR return from accept should
force continue rather than break in handling loop.
fail_on_fdne() is now file_exists() with a slightly different API.
20040818
Use inet_aton rather than custom function; daemon.[ch] removed.
20040817
ifchd no longer logs a "FATAL - select returned an error!" when it
is -KILL'ed.
20040626
pending_exit is now static volatile sig_atomic_t rather than
static volatile int for pedantic correctness issues.
20040614
Added --interface (-i) option that allows one to restrict the
interfaces that ifchd clients are allowed to modify. I
reccomend that this flag be used to further mitigate the possible
effects of a compromised client. By default, all interfaces
may be modified by clients.
Minor cleanups.
Clear corresponding namesvrs and domains on socket disconnection.
20040613
Factor out Linux-specific code into linux.c.
Nameservers and search domains now tracked per-connection to
prevent races where a client could force a writeout of data
provided by another client.
Interface name now cleared on connection close.
Make all headers idempotent.
Minor improvements to error messages.
20040612
Removed iffd[] array; this change makes the state machine action
functions (perform_*) depend on less external state.
HOSTNAME command now supported; it is not enabled by default.
If you wish for remote daemons to be able to change the hostname
of the local machine, use the --hostname (-o) option.
20040610
Added MTU support.
20040609
Robustify so that suicide() isn't called at every possible failure.
Harmless failures will now simply print an error to the log. Risky
or severe errors still suicide().
20040608
Added support for resolv.conf, namely "nameserver" and "search" entries.
Make strlist more robust and paranoid.
20040607
Improved accept() code to be much more robust; it can now properly error
recover. I hope this will fix the elusive random-exit problem that
plagues machines running the 2.6 kernel.
Refactored dispatch_work() to be cleaner.

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ifchd/ifchd.8 Normal file
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@ -0,0 +1,91 @@
.TH IFCHD 8 2011-07-12 Linux "Linux Administrator's Manual"
.SH NAME
ifchd \- interface change daemon
.SH SYNOPSIS
.B ifchd
.RI [ OPTION ]...
.SH DESCRIPTION
The ifchd daemon changes network interface configuration information
(such as the IP address, broadcast address, subnet, etc) as well as
resolv.conf, the machine hostname, and other similar system configuration
bits on the request of authorized clients such as ndhc instances.
.SH OPTIONS
.TP
.BR \-d ,\ \-\-detach
Immediately fork into the background. This is the default behavior.
.TP
.BR \-n ,\ \-\-nodetach
Do not fork into the background. Useful for debugging or initial setup.
.TP
.BR \-q ,\ \-\-quiet
Don't print to standard out, standard error, or syslog.
.TP
.BI \-c\ CHROOTDIR ,\ \-\-chroot= CHROOTDIR
This option specifies the directory to which ifchd should confine itself via
chroot() after startup. This directory should be shared with associated ndhc
daemons, and should have access to dev/urandom and dev/null. For logging to
work, a dev/log socket or device should also exist.
.TP
.BI \-r\ RESOLVCONF ,\ \-\-resolve= RESOLVCONF
Specifies the path to the system resolv.conf. This file will typically be in
/etc/resolv.conf. If this option is specified, ndhc will update the contents
of this file to match the DNS servers specified by the remote DHCP server. If
this option is not specified, ifchd will never change the system DNS resolution
configuration.
.TP
.BR \-o ,\ \-\-hostname
If specified, ifchd will update the system host name in response to any
hostname option field provided by a remote DHCP server on the request of
a ndhc client. If this option is not specified, ifchd will never change
the system hostname.
.TP
.BI \-p\ PIDFILE ,\ \-\-pidfile= PIDFILE
Write the process id number of the ifchd instance into the specified file name.
The default is to not write the process id number into any file at all.
.TP
.BI \-u\ USER ,\ \-\-user= USER
This option specifies the user name or user id that ifchd will change to after
startup. This user should be unique to the ifchd daemon.
.TP
.BI \-g\ GROUP ,\ \-\-group= GROUP
This option specifies the group name or group id that ifchd will change to
after startup.
.TP
.BI \-U\ CLIENTUSER ,\ \-\-cuser= CLIENTUSER
This option specifies the user name or user id that will be required of
processes that wish to make interface change requests of ifchd. Any other
users will be denied a connection to the ifchange socket.
.TP
.BI \-G\ CLIENTGROUP ,\ \-\-cgroup= CLIENTGROUP
This option specifies the group name or group id that will be required of
processes that wish to make interface change requests of ifchd. Any other
groups will be denied a connection to the ifchange socket.
.TP
.BI \-P\ CLIENTPID ,\ \-\-cpid= CLIENTPID
This option specifies the process id that will be required to make interface
change requests of ifchd. Any process that has a process id that does not
equal this value will be denied a connection to the ifchange socket.
.TP
.BI \-i\ INTERFACE ,\ \-\-interface= INTERFACE
Specifies an interface by name (such as 'eth0') on which ifchd is allowed to
make configuration changes (such as IP address, subnet mask, etc). Multiple
interfaces may be whitelisted by using this switch multiple times.
.TP
.BR \-V ,\ \-\-verbose
Print detailed messages. Useful for debugging or setup.
.TP
.BR \-h ,\ \-\-help
Print basic help information and exit.
.TP
.BR \-v ,\ \-\-version
Display the ifchd version number and copyright information.
.SH SIGNALS
It is not necessary to sleep between sending signals, as signals received are
processed sequentially in the order they are received. ifchd does not
perform any unusual behavior on receipt of signals.
.SH NOTES
ifchd is rather minimal and doesn't do exotic things like change NTP server
configuration. This is intentional, since it needs to run as CAP_NET_ADMIN,
which although far less powerful than root, still gives it a fair amount
of privileged behavior.

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@ -1,339 +0,0 @@
GNU GENERAL PUBLIC LICENSE
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA
Everyone is permitted to copy and distribute verbatim copies
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END OF TERMS AND CONDITIONS
Appendix: How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
<one line to give the program's name and a brief idea of what it does.>
Copyright (C) 19yy <name of author>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License. Of course, the commands you use may
be called something other than `show w' and `show c'; they could even be
mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program
`Gnomovision' (which makes passes at compilers) written by James Hacker.
<signature of Ty Coon>, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library. If this is what you want to do, use the GNU Library General
Public License instead of this License.

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@ -1,64 +0,0 @@
ndhc client
--------------------
The ndhc client negotiates a lease with the DHCP server and notifies
ifchd when a leases is obtained or lost.
command line options
-------------------
The command line options for the ndhc client are:
-c, --clientid=CLIENTID Client identifier
-H, --hostname=HOSTNAME Client hostname
-h, Alias for -H
-f, --foreground Do not fork after getting lease
-b, --background Fork to background if lease cannot be
immediately negotiated.
-i, --interface=INTERFACE Interface to use (default: eth0)
-n, --now Exit with failure if lease cannot be
immediately negotiated.
-q, --quit Quit after obtaining lease
-r, --request=IP IP address to request (default: none)
-v, --version Display version
If the requested IP address cannot be obtained, the client accepts the
address that the server offers.
note on ndhc's random seed
---------------------------
ndhc will seed its random number generator (used for generating xids)
by reading /dev/urandom. If you have a lot of embedded systems on the same
network, with no entropy, you can either seed /dev/urandom by a method of
your own, or doing the following on startup:
ifconfig eth0 > /dev/urandom
in order to seed /dev/urandom with some data (mac address) unique to your
system. If reading /dev/urandom fails, ndhc will fall back to its old
behavior of seeding with time(0).
signals accepted by ndhc
-------------------------
ndhc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,
and SIGUSR2 will force a release of the current lease, and cause ndhc to
go into an inactive state (until it is killed, or receives a SIGUSR1). You do
not need to sleep between sending signals, as signals received are processed
sequentially in the order they are received.
DHCP pitfalls
-------------
Send a packet that has an options field set to:
DHCP-OPTION-OVERLOAD:3
Then in the file and sname fields:
DHCP-OPTION-OVERLOAD:3
I suspect some bad dhcp programs will hang given this input.

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@ -1,46 +1,93 @@
.TH NDHC 8 2004-02-25 Linux "Linux Administrator's Manual"
.TH NDHC 8 2011-07-12 Linux "Linux Administrator's Manual"
.SH NAME
ndhc \- secure DHCP client
.SH SYNOPSIS
.B ndhc
.RI [ OPTION ]...
.SH DESCRIPTION
The ndhc client negotiates a lease with the DHCP server and
informs ifchd of the change when it is obtained or lost.
The ndhc client negotiates a lease with the DHCP server and informs ifchd of
the change when it is obtained or lost. It also defends the assigned IP
address against hostile imposters and requests a new lease if it detects that
the interface has been connected to a new network. It requires a cooperating
ifchd server to properly perform its duties.
.SH OPTIONS
.TP
.BI \-c\ CLIENTID ,\ \-\-clientid= CLIENTID
Send the client identifier
.IR CLIENTID .
Specifies the client identifier that will be sent to the remote server. This
can be any (reasonably sized, <64byte or so) text string, or an ethernet
MAC address in a form similar to 'aa:bb:cc:dd:ee:ff'. ndhc is smart enough
to recognize MAC addresses. ISP DHCP servers commonly check the value of this
field before providing a lease. The default value is the MAC address of
the network interface to which ndhc is bound.
.TP
.BR -f ,\ \-\-foreground
Do not fork after obtaining a lease.
.BI \-h\ HOSTNAME ,\ \-\-hostname= HOSTNAME
Send the specified client hostname to the remote DHCP server. This option
should not be necessary in most instances, but may perhaps be useful for odd
DHCP servers that perform some kind of authentication against the hostname
option field. The default is to send no hostname option at all.
.TP
.BI \-H\ HOSTNAME ,\ \-\-hostname= HOSTNAME
Send the client hostname
.IR HOSTNAME .
.BI \-v\ VENDORID ,\ \-\-vendorid= VENDORID
Send the specified vendor identification string to the remote DHCP server.
This option should not be necessary in most instances, but may perhaps be
useful for odd DHCP servers that perform some kind of authentication against
the vendor id option field. The default is to send the string 'ndhc'.
.TP
.BI \-h\ HOSTNAME
Alias for -H
.IR HOSTNAME .
.BR \-f ,\ \-\-foreground
Do not fork into the background after obtaining a lease.
.TP
.BR \-b ,\ \-\-background
Immediately fork into the background, even before obtaining a lease.
.TP
.BI \-p\ PIDFILE ,\ \-\-pidfile= PIDFILE
Write the process id number of the ndhc instance into the specified file name.
The default is to not write the process id number into any file at all.
.TP
.BI \-l\ LEASEFILE ,\ \-\-leasefile= LEASEFILE
Write the IP address of the currently held DHCP lease into the specified file
name. The default is to not write the lease IP address into any file at all.
This file can be quite useful for reacting to changes in IP address -- one
can listen for changes to it using fanotify() or inotify() on Linux.
.TP
.BI \-i\ INTERFACE ,\ \-\-interface= INTERFACE
Configure
.IR INTERFACE .
Act as a DHCP client for the specified interface. A single ndhc daemon can
only act as a DHCP client for a single interface. Specify the interface it
should use by name. The default is to listen on 'eth0'.
.TP
.BR -n ,\ \-\-now
Exit with failure if a lease cannot be obtained.
.BR \-n ,\ \-\-now
Exit with failure if a lease cannot be obtained. Useful for some init scripts.
.TP
.BR -q ,\ \-\-quit
Exit after obtaining a lease.
.BR \-q ,\ \-\-quit
Exit after obtaining a lease. Useful for some init scripts.
.TP
.BI \-r\ ADDRESS ,\ \-\-request= ADDRESS
Request IP address
.IR ADDRESS .
.BI \-r\ IP ,\ \-\-request= IP
Request the specified IP address from the remote DHCP server. The DHCP server
has no obligation to provide us with this IP, but it may acquiesce to the
request if it would not conflict with another host.
.TP
.BR -v ,\ \-\-version
Display version.
.SH NOTES
.BI \-u\ USER ,\ \-\-user= USER
This option specifies the user name or user id that ndhc will change to after
startup. ndhc will also change its group to match the default group of this
user. This user should have the ability to write to the ifchd socket of the
associated ifchd daemon. In practice, this requirement means that this user
should belong to the same group as the ifchd user.
.TP
.BI \-C\ CHROOTDIR ,\ \-\-chroot= CHROOTDIR
This option specifies the directory to which ndhc should confine itself via
chroot() after startup. This directory should be shared with the associated
ifchd daemon, and should have access to dev/urandom and dev/null. For
logging to work, a dev/log socket or device should also exist.
.TP
.BR \-d ,\ \-\-relentless-defense
If specified, ndhc will never back down in defending the IP address that it
has been assigned by the remote DHCP server. This behavior should not be
specified for average machines, but is useful for servers or routers where
the IP address of the machine must remain fixed for proper operation.
.TP
.BR \-v ,\ \-\-version
Display the ndhc version number.
.SH SIGNALS
It is not necessary to sleep between sending signals, as signals received are
processed sequentially in the order they are received.
.B ndhc
responds to the following signals:
.TP
@ -51,6 +98,18 @@ to renew the current lease or, if it does not have one, obtain a
new lease.
.TP
.B SIGUSR2
This signal caused
This signal causes
.B ndhc
to release the current lease.
to release the current lease and go to sleep until it receives a SIGUSR1.
.SH NOTES
ndhc will seed its random number generator (used for generating xids)
by reading /dev/urandom. If you have a lot of embedded systems on the same
network, with no entropy, you can either seed /dev/urandom by a method of
your own, or doing the following on startup:
ifconfig eth0 > /dev/urandom
in order to seed /dev/urandom with some data (mac address) unique to your
system. If reading /dev/urandom fails, ndhc will fall back to seeding with
time(0).

View File

@ -79,6 +79,8 @@ struct client_config_t client_config = {
static void show_usage(void)
{
printf(
"ndhc " VERSION ", dhcp client. Licensed under GNU GPL.\n"
"Copyright (C) 2004-2011 Nicholas J. Kain\n"
"Usage: ndhc [OPTIONS]\n\n"
" -c, --clientid=CLIENTID Client identifier\n"
" -h, --hostname=HOSTNAME Client hostname\n"
@ -312,7 +314,12 @@ int main(int argc, char **argv)
arp_relentless_def = 1;
break;
case 'v':
printf("ndhc, version " VERSION "\n\n");
printf(
"ndhc %s, dhcp client. Licensed under GNU GPL.\n", VERSION);
printf(
"Copyright (C) 2004-2011 Nicholas J. Kain\n"
"This is free software; see the source for copying conditions. There is NO\n"
"WARRANTY; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n");
exit(EXIT_SUCCESS);
break;
case 'V':