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vsftpd-1.1.3配制实例之五:VIRTUAL_USERS

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

This example shows how to set up vsFTPd / PAM with "virtual users".

A virtual user is a user login which does not exist as a real login on the

system. Virtual users can therefore be more secure than real users, beacuse

a compromised account can only use the FTP server.

Virtual users are often used to serve content that should be Accessible to untrusted users, but not generally accessible to the public.

Step 1) Create the virtual users database.

We are going to use pam_userdb to authenticate the virtual users. This needs

a username / passWord file in "db" format - a common database format.

To create a "db" format file, first create a plain text files with the

usernames and password on alternating lines.

See example file "logins.txt" - this specifies "tom" with password "foo" and

"fred" with password "bar".

Whilst logged in as root, create the actual database file like this:

db_load -T -t hash -f logins.txt /etc/vsftpd_login.db

(Requires the Berkeley db program installed).

This will create /etc/vsftpd_login.db. Obviously, you may want to make sure

the permissions are restricted:

chmod 600 /etc/vsftpd_login.db

For more information on maintaing your login database, look around for

documentation on "Berkeley DB", e.g.

http://www.sleepycat.com/docs/utility/index.Html

Step 2) Create a PAM file which uses your new database.

See the example file vsftpd.pam. It contains two lines:

auth required /lib/security/pam_userdb.so db=/etc/vsftpd_login

account required /lib/security/pam_userdb.so db=/etc/vsftpd_login

This tells PAM to authenticate users using our new database. Copy this PAM

file to the PAM Directory - typically /etc/pam.d/

cp vsftpd.pam /etc/pam.d/ftp

Step 3) Set up the location of the files for the virtual users.

useradd -d /home/ftpsite virtual

ls -ld /home/ftpsite

(which should give):

drwx------ 3 virtual virtual 4096 Jul 30 00:39 /home/ftpsite

We have created a user called "virtual" with a home directory "/home/ftpsite".

Let's add some content to this download area:

cp /etc/hosts /home/ftpsite

chown virtual.virtual /home/ftpsite/hosts

Step 4) Create your vsftpd.conf config file.

See the example in this directory. Let's go through it line by line:

anonymous_enable=NO

local_enable=YES

This disables anonymous FTP for security, and enables non-anonymous FTP (which

is what virtual users use).

write_enable=NO

anon_upload_enable=NO

anon_mkdir_write_enable=NO

anon_other_write_enable=NO

These ensure that for security purposes, no write commands are allowed.

chroot_local_user=YES

This makes sure that the virtual user is restricted to the virtual FTP area

/home/ftpsite we set up above.

guest_enable=YES

guest_username=virtual

The guest_enable is very important - it activates virtual users!

And

guest_username says that all virtual users are mapped to the real user

"virtual" that we set up above. This will also determine where on the

filesystem the virtual users end up - the home directory of the user

"virtual", /home/ftpsite.

listen=YES

listen_port=10021

This puts vsftpd in "standalone" mode - i.e. not running from an inetd. This

means you just run the vsftpd executable and it will start up. This also

makes vsftpd listen for FTP requests on the non-standard port of 10021 (FTP

is usually 21).

pasv_min_port=30000

pasv_max_port=30999

These put a port range on passive FTP incoming requests - very useful if

you are configuring a firewall.

Copy the example vsftpd.conf file to /etc:

cp vsftpd.conf /etc/

Step 5) Start up vsftpd.

Go to the directory with the vsftpd binary in it, and:

./vsftpd

If all is well, the command will sit there. If all is not well, you will

likely see some error message.

Step 6) Test.

Launch another shell session (or background vsftpd with CTRL-Z and then "bg").

Here is an example of an FTP session:

ftp localhost 10021

Connected to localhost (127.0.0.1).

220 ready, dude (vsFTPd 1.1.0: beat me, break me)

Name (localhost:chris): tom

331 Please specify the password.

Password:

230 Login sUCcessful. Have fun.

Remote system type is UNIX.

Using binary mode to transfer files.

ftp pwd

257 "/"

ftp ls

227 Entering Passive Mode (127,0,0,1,117,135)

150 Here comes the directory listing.

226 Transfer done (but failed to open directory).

ftp size hosts

213 147

ftp

Comments:

The password we gave was "foo".

Do not be alarmed by the "failed to open directory". That is because the

directory /home/ftpsite is not world readable (we could change this

behaviour if we wanted using anon_world_readable_only=NO but maybe we want

it this way for security.

We can see that we have access to the "hosts" file we copied into the virtual

FTP area, via the size command.

logins.txt

tom

foo

fred

bar

vsftpd.conf

anonymous_enable=NO

local_enable=YES

write_enable=NO

anon_upload_enable=NO

anon_mkdir_write_enable=NO

anon_other_write_enable=NO

chroot_local_user=YES

guest_enable=YES

guest_username=virtual

listen=YES

listen_port=10021

pasv_min_port=30000

pasv_max_port=30999

vsftpd.pam

auth required /lib/security/pam_userdb.so db=/etc/vsftpd_login

account required /lib/security/pam_userdb.so db=/etc/vsftpd_login

VIRTUAL_USERS_2

This example shows how to extend the "VIRTUAL_USERS" example to reflect

a slightly more complex setup.

Let's assume that we want two types of virtual user - one that can only browse

and download content, and another that can upload new content as well as

download existing content.

To achieve this setup, we can use use of vsftpd's powerful per-user

configurability (new in v1.1.0).

In the previous virtual user example, we created two users - tom and fred.

Let's say that we want fred to have write access to upload new files whilst

tom can only download.

Step 1) Activate per-user configurability.

To activate this powerful vsftpd feature, add the following to

/etc/vsftpd.conf:

user_config_dir=/etc/vsftpd_user_conf

And, create this directory:

mkdir /etc/vsftpd_user_conf

Step 2) Give tom the ability to read all files / directories.

At the end of the last example, we noted that the virtual users can only

see world-readable files and directories. We could make the /home/ftpsite

directory world readable, and upload files with world-read permission. But

another way of doing this is giving tom the ability to download files which

are not world-readable.

For the tom user, supply a config setting override for

anon_world_readable_only:

echo "anon_world_readable_only=NO" /etc/vsftpd_user_conf/tom

Check it out - login as tom and now "ls" will return a directory listing!

Log in as fred and it won't.

NOTE - restart vsftpd to pick up the config setting changes to

/etc/vsftpd.conf. (Advanced users can send SIGHUP to the vsftpd listener

process).

Step 3) Give fred the ability to read all files / directories and create

new ones but not interfere with existing files.

echo "anon_world_readable_only=NO" /etc/vsftpd_user_conf/fred

echo "write_enable=YES" /etc/vsftpd_use

 
 
 
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