akvlad / ftp-to-ssh

FTP2SSH - FTP Over a Plain Console

FTP2SSH - FTP Over a Plain Console

FTP2SSH is a utility allowing to convert a plain bash access to file system to an FTP server in case of scp/sftp/smb absence. For example in case of access via kubernetes access or ongoing suppression of scp/sftp for whatever reasons.

Getting started

1. Download dist directory to a local folder.
2. Create "configuration.json" file: {"spawn": "<command to spawn a bash console>", "exit": "<command to exit the bash console>", "host": "127.0.0.1"}
3. Run ./start.sh or java -jar ftp2Ssh-0.0.1-SNAPSHOT.jar
4. Open Filezilla to localhost:8888 with a random login/password.
5. Use an ftp access.

Prerequisites

For the system where utility will be started:

• JAVA 1.8+

For the system which will access it over a bash-like console (ssh/kubectl/etc):

• base64
• split
• ls
• cat
• echo
• stat
• mkdir
• rm
• mv
• gzip (optional)

File transfer process

During the execution of STOR command files are read chunk by chunk. Each chunk then gets base64 encoded and stored in temporary folder as files. After the last chunk is stored, the command to merge all of the chunks into the destination file is executed.

RERT command encodes the remote file, then splits it into chunks and stores each chunk in the temporary folder. Then the utility reads each chunk and transfers it according to the requirements of ftp protocol.

In gzip mode utility compresses each chunk before base64 encoding.

Configurations

General configurations

Parameter	Type	Default / Example	Description
port	int	8888	Port to listen
host	String	0.0.0.0	Hostname to listen
spawn	String	sshpass -p {{PASS}} ssh {{USER}}@127.0.0.1 (Default: bash)	Command to spawn a new console. Available parameters {{USER}} - login of the ftp user, {{PASS}} - password of the ftp user
chunkSize	int	10000	Amount of data in bytes to transfer at once. Should not be too big as it is written by echo "..." >>... by default.
tmpFolder	String	/tmp	Folder to store chunks of the file to transfer. Has to be writable for the spawned bash session.
timeoutSec	int	30	Timeout in seconds for a command to execute or for a chunk to transfer.
maxLayers	int	10	Maximum of spawned bash sessions for one ftp session. Minimum is 2.
gzip	boolean	false	Use gzip to archive data before sending it over a console.

Configurations to overwrite commands

Parameter	Type	Default / Example	Description
prepareFileToRetr	String	base64 -w {{CHUNK_SIZE}} {{FILE}} | split -l 1 - {{TMP}}{{DS}}	Command to split a remote file to retrieve. The command should create a set of files in the temporary folder to retrieve in alphabetical order. Each file has to be base64 encoded. {{CHUNK_SIZE}} - size of a chunk in bytes, {{FILE}} - file to retrieve {{TMP}} - temporary folder to split a file {{DS}} - directory separator
fileSlice	String	dd "if={{FROM}}" "of={{TO}}" bs={{SLICE_SIZE}} count={{SLICE_COUNT}} skip={{SLICE_OFFSET}}	Command to copy part of a remote file. {{FROM}} - name of a file, {{TO}} - where to copy {{SLICE_SIZE}} - size of a chunk {{SLICE_COUNT}} - number of chunks to copy {{SLICE_OFFSET}} - number of chunks to offset from the file start {{SIZE}} - number of bytes to copy (SLICE_SIZE * SLICE_COUNT) {{OFFSET}} - number of bytes to skip from the start (SLICE_SIZE * SLICE_OFFSET)
retrPiece	String	cat {{FILE}}	Command to print a chunk to stdout. {{FILE}} - the name of the file to print
storePiece	String	echo {{PIECE}} >>{{TMPFILE}}	Command to store a chunk of data. {{PIECE}} - a base64 encoded chunk {{TMPFILE}} - name of the file to store
joinStoredPieces	String	base64 -d {{TMPFILE}} >>{{FILE}}	Base64 decode a chunk and store it to the file. {{TMPFILE}} - name of the file storing the chunk {{FILE}} - name of the destination file
echo	String	echo	Print something to stdout. Used as echo "Some escaped text"
cd	String	cd	Change directory. Used as cd "/escaped/path"
pwd	String	pwd	Print current directory.
lsla	String	ls -la --time-style="+%Y-%m-%dT%H:%M"	Enumerate files in directory. Used as ls -la --time-style="+%Y-%m-%dT%H:%M" "/escaped/path".
lsw1	String	ls -w1	Print files in directory one per line. Used as ls -w1 "/escaped/path".
size	String	stat {{FILE}} | grep -oEh "Size: [0-9]+" | cut -b 7-	Print file size in bytes. {{FILE}} - filename to get size
mkdir	String	mkdir	Create directory. Used as mkdir "/path/to/directory".
mv	String	mv {{FROM}} {{TO}}	Move file. {{FROM}} - filename to move. {{TO}} - destination path
rmrf	String	rm -rf	Remove a file or a directory recursively. Used as rm -rf "/path/to/remove"
exit	String	exit	Gracefully close the console.
DS	String	/	Directory Separator.

GZIP compression

If gzip configuration is set to true, the utility assumes that chunks are gzipped before transfer. Chunks stored in the temporary folder during STOR will be gzipped and base64 encoded. Also each chunk has to be gzipped and base64 encoded before RETR.

Default commands in gzip mode:

Command	Default
joinStoredPieces	base64 -d {{TMPFILE}} | gzip -d -c - >>{{FILE}}
prepareFileToRetr	split -b {{CHUNK_SIZE}} --additional-suffix .split {{FILE}} {{TMP}}{{DS}} && gzip {{TMP}}{{DS}}* && for l in `ls {{TMP}}`; do base64 {{TMP}}{{DS}}$l >{{TMP}}{{DS}}$l.b64; done && rm {{TMP}}{{DS}}*.split.gz

Examples

Ftp over bash to the local computer. Just for example.

{
	"spawn": "bash",
	"host": "0.0.0.0",
	"exit": "exit"
}

---

Ftp over ssh to remote computer. In case of scp/sftp is disabled somehow.

{
	"spawn": "sshpass -p {{PASS}} ssh {{USER}}@127.0.0.1",
	"host": "0.0.0.0",
	"exit": "exit"
}

---

Bash over kubectl, which is my use case. Create file sh-pod.sh:

#!/bin/bash
l=`kubectl get pods | grep $1 | cut --delimiter=' ' -f1`; 
kubectl exec $l -it sh

Add execution mode to the file: chmod +x sh-pod.sh

Configuration file:

{
	"spawn": "./sh-pod.sh {{USER}}",
	"host": "0.0.0.0",
	"exit": "exit"
}

Don't forget to start the utility from its directory or to specify the full path to the sh-pod file.

TODO:

• Bash injections. Some injections similar to mkdir "$(rm -rf /)"` or `rm "`whoami`" are escaped, but this still requires some investigation.
• Windows support. Have not been tested yet.
• Better way to stor/retr files. Currently working with big files is impossible.