view dropbear.8 @ 1306:34e6127ef02e

merge fixes from PuTTY import.c toint() from misc.c (revids are from hggit conversion) changeset: 4620:60a336a6c85c user: Simon Tatham <[email protected]> date: Thu Feb 25 20:26:33 2016 +0000 files: import.c description: Fix potential segfaults in reading OpenSSH's ASN.1 key format. The length coming back from ber_read_id_len might have overflowed, so treat it as potentially negative. Also, while I'm here, accumulate it inside ber_read_id_len as an unsigned, so as to avoid undefined behaviour on integer overflow, and toint() it before return. Thanks to Hanno Böck for spotting this, with the aid of AFL. (cherry picked from commit 5b7833cd474a24ec098654dcba8cb9509f3bf2c1) Conflicts: import.c (cherry-picker's note: resolving the conflict involved removing an entire section of the original commit which fixed ECDSA code not present on this branch) changeset: 4619:9c6c638d98d8 user: Simon Tatham <[email protected]> date: Sun Jul 14 10:45:54 2013 +0000 files: import.c ssh.c sshdss.c sshpubk.c sshrsa.c description: Tighten up a lot of casts from unsigned to int which are read by one of the GET_32BIT macros and then used as length fields. Missing bounds checks against zero have been added, and also I've introduced a helper function toint() which casts from unsigned to int in such a way as to avoid C undefined behaviour, since I'm not sure I trust compilers any more to do the obviously sensible thing. [originally from svn r9918] changeset: 4618:3957829f24d3 user: Simon Tatham <[email protected]> date: Mon Jul 08 22:36:04 2013 +0000 files: import.c sshdss.c sshrsa.c description: Add an assortment of extra safety checks. [originally from svn r9896] changeset: 4617:2cddee0bce12 user: Jacob Nevins <[email protected]> date: Wed Dec 07 00:24:45 2005 +0000 files: import.c description: Institutional failure to memset() things pointed at rather than pointers. Things should now be zeroed and memory not leaked. Spotted by Brant Thomsen. [originally from svn r6476] changeset: 4616:24ac78a9c71d user: Simon Tatham <[email protected]> date: Wed Feb 11 13:58:27 2004 +0000 files: import.c description: Jacob's last-minute testing found a couple of trivial bugs in import.c, and my attempts to reproduce them in cmdgen found another one there :-) [originally from svn r3847] changeset: 4615:088d39a73db0 user: Simon Tatham <[email protected]> date: Thu Jan 22 18:52:49 2004 +0000 files: import.c description: Placate some gcc warnings. [originally from svn r3761] changeset: 4614:e4288bad4d93 parent: 1758:108b8924593d user: Simon Tatham <[email protected]> date: Fri Oct 03 21:21:23 2003 +0000 files: import.c description: My ASN.1 decoder returned wrong IDs for anything above 0x1E! Good job it's never had to yet. Ahem. [originally from svn r3479]
author Matt Johnston <matt@ucc.asn.au>
date Tue, 12 Jul 2016 23:00:01 +0800
parents 80cacacfec23
children ee2ffa044c7e
line wrap: on
line source

.TH dropbear 8
.SH NAME
dropbear \- lightweight SSH server
.SH SYNOPSIS
.B dropbear
[\fIflag arguments\fR] [\-b
.I banner\fR] 
[\-r
.I hostkeyfile\fR] [\-p [\fIaddress\fR:]\fIport\fR]
.SH DESCRIPTION
.B dropbear
is a small SSH server 
.SH OPTIONS
.TP
.B \-b \fIbanner
bannerfile.
Display the contents of the file
.I banner
before user login (default: none).
.TP
.B \-r \fIhostkey
Use the contents of the file
.I hostkey
for the SSH hostkey.
This file is generated with
.BR dropbearkey (1) 
or automatically with the '-R' option. See "Host Key Files" below.
.TP
.B \-R
Generate hostkeys automatically. See "Host Key Files" below.
.TP
.B \-F
Don't fork into background.
.TP
.B \-E
Log to standard error rather than syslog.
.TP
.B \-m
Don't display the message of the day on login.
.TP
.B \-w
Disallow root logins.
.TP
.B \-s
Disable password logins.
.TP
.B \-g
Disable password logins for root.
.TP
.B \-j
Disable local port forwarding.
.TP
.B \-k
Disable remote port forwarding.
.TP
.B \-p\fR [\fIaddress\fR:]\fIport
Listen on specified 
.I address
and TCP
.I port.
If just a port is given listen
on all addresses.
up to 10 can be specified (default 22 if none specified).
.TP
.B \-i
Service program mode.
Use this option to run
.B dropbear
under TCP/IP servers like inetd, tcpsvd, or tcpserver.
In program mode the \-F option is implied, and \-p options are ignored.
.TP
.B \-P \fIpidfile
Specify a pidfile to create when running as a daemon. If not specified, the 
default is /var/run/dropbear.pid
.TP
.B \-a
Allow remote hosts to connect to forwarded ports.
.TP
.B \-W \fIwindowsize
Specify the per-channel receive window buffer size. Increasing this 
may improve network performance at the expense of memory use. Use -h to see the
default buffer size.
.TP
.B \-K \fItimeout_seconds
Ensure that traffic is transmitted at a certain interval in seconds. This is
useful for working around firewalls or routers that drop connections after
a certain period of inactivity. The trade-off is that a session may be
closed if there is a temporary lapse of network connectivity. A setting
if 0 disables keepalives. If no response is received for 3 consecutive keepalives the connection will be closed.
.TP
.B \-I \fIidle_timeout
Disconnect the session if no traffic is transmitted or received for \fIidle_timeout\fR seconds.
.TP
.B \-V
Print the version

.SH FILES

.TP
Authorized Keys

~/.ssh/authorized_keys can be set up to allow remote login with a RSA,
ECDSA, or DSS
key. Each line is of the form
.TP
[restrictions] ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIgAsp... [comment]

and can be extracted from a Dropbear private host key with "dropbearkey -y". This is the same format as used by OpenSSH, though the restrictions are a subset (keys with unknown restrictions are ignored).
Restrictions are comma separated, with double quotes around spaces in arguments.
Available restrictions are:

.TP
.B no-port-forwarding
Don't allow port forwarding for this connection

.TP
.B no-agent-forwarding
Don't allow agent forwarding for this connection

.TP
.B no-X11-forwarding
Don't allow X11 forwarding for this connection

.TP
.B no-pty
Disable PTY allocation. Note that a user can still obtain most of the
same functionality with other means even if no-pty is set.

.TP
.B command=\fR"\fIforced_command\fR"
Disregard the command provided by the user and always run \fIforced_command\fR.

The authorized_keys file and its containing ~/.ssh directory must only be
writable by the user, otherwise Dropbear will not allow a login using public
key authentication.

.TP
Host Key Files

Host key files are read at startup from a standard location, by default
/etc/dropbear/dropbear_dss_host_key, /etc/dropbear/dropbear_rsa_host_key, and 
/etc/dropbear/dropbear_ecdsa_host_key
or specified on the commandline with -r. These are of the form generated
by dropbearkey. The -R option can be used to automatically generate keys
in the default location - keys will be generated after startup when the first
connection is established. This had the benefit that the system /dev/urandom
random number source has a better chance of being securely seeded.

.TP
Message Of The Day

By default the file /etc/motd will be printed for any login shell (unless 
disabled at compile-time). This can also be disabled per-user
by creating a file ~/.hushlogin .

.SH ENVIRONMENT VARIABLES
Dropbear sets the standard variables USER, LOGNAME, HOME, SHELL, PATH, and TERM.

The variables below are set for sessions as appropriate. 

.TP
.B SSH_TTY
This is set to the allocated TTY if a PTY was used.

.TP
.B SSH_CONNECTION
Contains "<remote_ip> <remote_port> <local_ip> <local_port>".

.TP
.B DISPLAY
Set X11 forwarding is used.

.TP
.B SSH_ORIGINAL_COMMAND
If a 'command=' authorized_keys option was used, the original command is specified
in this variable. If a shell was requested this is set to an empty value.

.TP
.B SSH_AUTH_SOCK
Set to a forwarded ssh-agent connection.

.SH NOTES
Dropbear only supports SSH protocol version 2.

.SH AUTHOR
Matt Johnston ([email protected]).
.br
Gerrit Pape ([email protected]) wrote this manual page.
.SH SEE ALSO
dropbearkey(1), dbclient(1), dropbearconvert(1)
.P
https://matt.ucc.asn.au/dropbear/dropbear.html