Provided by: libnet-sftp-sftpserver-perl_1.1.0-4_all 
NAME
Net::SFTP::SftpServer - A Perl implementation of the SFTP subsystem with user access
controls
SYNOPSIS
use Net::SFTP::SftpServer;
my $sftp = Net::SFTP::SftpServer->new();
$sftp->run();
DESCRIPTION
A Perl port of sftp-server from openssh providing access control on a per user per command
basis and improved logging via syslog
The limitations compared with the openssh implementation are as follows:
• Only files and directories are dealt with - other types are not returned on readdir
• a virtual chroot is performed - / is treated as the users home directory from the
client perspective and all file access to / will be in /<home_path>/<username>
home_path is defined on object initialisation not accessed from /etc/passwd The script
DOES NOT run under chroot - this prevents it needing SUID to start. The virtual
chroot is enforced by the objects and prevent opperations outside the home area
• all sym linked files or directories are hidden and not accessible on request
• symlink returns permission denied. Please contact me if you need this functionaility
implementing
• readlink returns file does not exist. Please contact me if you need this
functionaility implementing
• setting of stats (set_stat or set_fstat) is disabled - client will receive permission
denied. Please contact me if you need this functionaility implementing
• permissions for file or dir is defaulted - default set on object initialisation
USAGE
Basic usage:
use Net::SFTP::SftpServer;
Import options:
:LOG - Import logging functions for use in callbacks
:ACTION - Import constants for Allow/Deny of actions
Configuring syslog:
Syslog output mode must be configured in the use statement of the module as follows:
use Net::SFTP::SftpServer ( { log => 'local5' }, qw ( :LOG :ACTIONS ) );
Net::SFTP::SftpServer will default to using "daemon" see your system's syslog
documentation for more details
Options for object initialisation:
• debug
Log debug level information. Deault=0 (note this will create very large log files -
use with caution)
• home
Filesystem location of user home directories. default=/home
• file_perms
Octal file permissions to force on creation of files. Default=0666 or permissions
specified by file open command from client
• dir_perms
Octal dir permissions to force on creation of directories. Default=0777 or permissions
specified by mkdir command from client
• on_file_sent, on_file_received
References to callback functions to be called on complete file sent or received.
Function will be passed the full path and filename on the filesystem as a single
argument
• use_tmp_upload
Use temporary upload filenames while a file is being uploaded - this allows a
monitoring script to know which files are in transit without having to watch file
size. Will be done transparantly to the user, the file will be renamed to the
original file name when close. The temportary extension is ".SftpXFR.$$". Default=0
• max_file_size
Maximum file size (in bytes) which can be uploaded. Default=0 (no limit)
• valid_filename_char
Array of valid characters for filenames
• allow, deny
Actions allowed or denied - see "PERMISSIONS" for details, Default is to allow ALL.
• fake_ok
Array of actions (see action contants in "PERMISSIONS") which will be given response
SSH2_FX_OK instead of SSH2_FX_PERMISSION_DENIED when denied by above deny options.
Default=[]
• log_action_supress
Array of actions to log quietly (logDetail - syslog debug level), logs messages
whenever this action is performed. Default is quiet for SSH2_FXP_READ, SSH2_FXP_WRITE,
SSH2_FX_OPENDIR, SSH2_FXP_READDIR, SSH2_FXP_CLOSE, SSH2_FXP_STAT SSH2_FXP_FSTAT and
SSH2_FXP_LSTAT override with log_action, see below.
• log_action
Array of actions to log loudly (logGeneral - syslog info level), logs messages
whenever this action is performed.
• log_all_status
Log all status messages at info level. By default SSH2_FX_OK and SSH2_FX_EOF will be
logged at debug level.
PERMISSIONS
ALL - All actions
NET_SFTP_SYMLINKS - Symlinks in paths to files (recommended deny to enforce chroot)
NET_SFTP_RENAME_DIR - Rename directories (recommended deny if also denying SSH2_FXP_MKDIR)
SSH2_FXP_OPEN
SSH2_FXP_CLOSE
SSH2_FXP_READ
SSH2_FXP_WRITE
SSH2_FXP_LSTAT
SSH2_FXP_STAT_VERSION_0
SSH2_FXP_FSTAT
SSH2_FXP_SETSTAT - Automatically denied, not implemented in module
SSH2_FXP_FSETSTAT - Automatically denied, not implemented in module
SSH2_FXP_OPENDIR
SSH2_FXP_READDIR
SSH2_FXP_REMOVE
SSH2_FXP_MKDIR
SSH2_FXP_RMDIR
SSH2_FXP_STAT
SSH2_FXP_RENAME
SSH2_FXP_READLINK - Automatically denied, not implemented in module
SSH2_FXP_SYMLINK - Automatically denied, not implemented in module
CALLBACKS
Callback functions can be used to perform actions when files are sent or received, for
example move a fully downloaded file to a processed directory or move a received file into
an input directory. The callback is proided with a Net::SFTP::SftpServer::File object.
This object allows access to the file within the virtual chroot environment. It will also
return the full filename, or move the file to an explicit location on the full filesystem.
Either of these actions will break the chroot and the methods on the object will no longer
be available.
The following methods are provided
• read
Read the data from the file - as the IO::File->read. Will open the file for reading if
it is not already open and read back the data.
• open
Will open the file - as IO::File->open but the filename is not supplied.
• getFilename
Will return the filename as within the virtual chroot
• getFullFilenameBREAKCHROOT
Will return the full filename on the real file system and break the virtual chroot
• renameBREAKCHROOT
Takes a single argument of the new filename, will rename the file to that location and
break the virtual chroot
LOGGING
If :LOG is used when including Net::SFTP::SftpServer the following logging functions will
be available:
logError - syslog with a log level of error
logWarning - syslog with a log level of warning
logGeneral - syslog with a log level of info
logDetail - syslog with a log level of debug, unless object was created with debug=>1 then syslog with a level of info
HARDENED EXAMPLE SCRIPT
The following example script shows how this module can be used to give far greater control
over what is allowed on your SFTP server.
This setup is aimed at admins which want to user SFTP uploads but do not wish to grant
users a system account. You will also need to set both the SFTP subsystem and the user's
shell to the sftp script, eg /usr/local/bin/sftp-server.pl
This configuration:
• Enforces that users can only access the sftp script, not an ssh shell.
• Chroots them into their home directory in /var/upload/sftp
• Sets all file permissions to 0660 and does not permit users to change them.
• Does not allow symlinks, making directories or renaming directories, but allows all
other normal actions.
• Has a max upload filesize of 200Mb
• Has a script memory limit of 100Mb for safety
• Will log actions by user sftptest in debug mode
• Will only allow alphanumeric plus _ . and - in filenames
• Will call ActionOnSent and ActionOnReceived respectively when files have been sent or
received.
#!/usr/local/bin/perl
use strict;
use warnings;
use Net::SFTP::SftpServer ( { log => 'local5' }, qw ( :LOG :ACTIONS ) );
use BSD::Resource; # for setrlimit
use constant DEBUG_USER => {
SFTPTEST => 1,
};
# Security - make sure we have started this as sftp not ssh
unless ( scalar @ARGV == 2 and
$ARGV[0] eq '-c' and
($ARGV[1] eq '/usr/local/bin/sftp-server.pl') ){
logError "SFTP connection attempted for application $ARGV[0] - exiting";
print "\n\rYou do not have permission to login interactively to this host.\n\r\n\rPlease contact the system administrator if you believe this to be a configuration error.\n\r";
exit 1;
}
my $MEMLIMIT = 100 * 1024 * 1024; # 100 Mb
# hard limits on process memory usage;
setrlimit( RLIMIT_RSS, $MEMLIMIT, $MEMLIMIT );
setrlimit( RLIMIT_VMEM, $MEMLIMIT, $MEMLIMIT );
my $debug = (defined DEBUG_USER->{uc(getpwuid($>))} and DEBUG_USER->{uc(getpwuid($>))}) ? 1 : 0;
my $sftp = Net::SFTP::SftpServer->new(
debug => $debug,
home => '/var/upload/sftp',
file_perms => 0660,
on_file_sent => \&ActionOnSent,
on_file_received => \&ActionOnReceived,
use_tmp_upload => 1,
max_file_size => 200 * 1024 * 1024,
valid_filename_char => [ 'a' .. 'z', 'A' .. 'Z', '0' .. '9', '_', '.', '-' ],
deny => ALL,
allow => [ (
SSH2_FXP_OPEN,
SSH2_FXP_CLOSE,
SSH2_FXP_READ,
SSH2_FXP_WRITE,
SSH2_FXP_LSTAT,
SSH2_FXP_STAT_VERSION_0,
SSH2_FXP_FSTAT,
SSH2_FXP_OPENDIR,
SSH2_FXP_READDIR,
SSH2_FXP_REMOVE,
SSH2_FXP_STAT,
SSH2_FXP_RENAME,
)],
fake_ok => [ (
SSH2_FXP_SETSTAT,
SSH2_FXP_FSETSTAT,
)],
);
$sftp->run();
sub ActionOnSent {
my $fileObject = shift;
## Do Stuff
}
sub ActionOnReceived {
my $fileObject = shift;
## Do Stuff
}
DEPENDENCIES
Stat::lsMode
Fcntl
POSIX
Sys::Syslog
Errno
SEE ALSO
Sftp protocol <http://www.openssh.org/txt/draft-ietf-secsh-filexfer-02.txt>
AUTHOR
Simon Day, Pirum Systems Ltd
cpan <at> simonday.info
COPYRIGHT AND LICENSE
Based on sftp-server.c Copyright (c) 2000-2004 Markus Friedl. All rights reserved.
Ported to Perl and extended by Simon Day Copyright (c) 2009 Pirum Systems Ltd. All rights
reserved.
Permission to use, copy, modify, and distribute this software for any purpose with or
without fee is hereby granted, provided that the above copyright notice and this
permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT
SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR
ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE
USE OR PERFORMANCE OF THIS SOFTWARE.