vsftpd closes conntion with code 421 when listing directory content

Question

I am currently struggling with some kind of connection problem with vsftpd.

I am using an arch linux and have vsftpd version 3.0.3 installed.

I don't use iptables or anything. When I connect to my FTP server, I am successfully able to log in and browse directories. I am also able to up- and download files.

The FTP user is chrooted into his home directory, and all subdirectories are owned by the ftp user.

The current structure:

|- home_dir
   |- dir1
      |- dir2
         |- dir3
         |- dir3
         |- dir4
         |- ...

I am able to "cd" into dir1, do a "ls" and up / download files. I am also able to "cd" into dir2, but here comes the tricky part:

I can perfectly upload files into dir2, but when I do a "ls", the server is closing the connection saying: "421 Service not available, remote server has closed connection". I figured out, that the cause are several of the subdirectories of "dir2". I figured out, that the existence of 8 of all subdirectories are causing the connection to be closed. Once I remove them, the listing works fine. All names are containing lower letters from a to z, no special chars.

My ftp config:

log_ftp_protocol=YES
anonymous_enable=NO

userlist_enable=YES
userlist_file=/etc/vsftpd.user_list
userlist_deny=NO

pasv_addr_resolve=YES
pasv_address=mydomain.com
pasv_enable=Yes
pasv_min_port=40020
pasv_max_port=40030

local_enable=YES

write_enable=YES

local_umask=002

dirmessage_enable=YES

xferlog_enable=YES

connect_from_port_20=YES


chown_uploads=YES
chown_username=myuser


ftpd_banner=Welcome.

chroot_local_user=YES

And that's what the servers FTP-Log says:

Wed Dec 28 13:55:06 2016 [pid 2] CONNECT: Client "<client_ip>"
Wed Dec 28 13:55:06 2016 [pid 2] FTP response: Client "<client_ip>", "220 Welcome."
Wed Dec 28 13:55:07 2016 [pid 2] FTP command: Client "<client_ip>", "USER myuser"
Wed Dec 28 13:55:07 2016 [pid 2] [myuser] FTP response: Client "<client_ip>", "331 Please specify the password."
Wed Dec 28 13:55:07 2016 [pid 2] [myuser] FTP command: Client "<client_ip>", "PASS <password>"
Wed Dec 28 13:55:07 2016 [pid 1] [myuser] OK LOGIN: Client "<client_ip>"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "230 Login successful."
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "OPTS UTF8 ON"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "200 Always in UTF8 mode."
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "PWD"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "257 "/" is the current directory"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "TYPE I"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "200 Switching to Binary mode."
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "PASV"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "227 Entering Passive Mode (<server_ip>,156,86)."
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "LIST"
Wed Dec 28 13:55:07 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "150 Here comes the directory listing."
Wed Dec 28 13:55:08 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "226 Directory send OK."
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "CWD /dir1"
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "250 Directory successfully changed."
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "PASV"
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "227 Entering Passive Mode (<server_ip>,156,92)."
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "LIST"
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "150 Here comes the directory listing."
Wed Dec 28 13:55:09 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "226 Directory send OK."
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "CWD /dir1/dir2"
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "250 Directory successfully changed."
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "PASV"
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "227 Entering Passive Mode (<server_ip>,156,87)."
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP command: Client "<client_ip>", "LIST"
Wed Dec 28 13:55:11 2016 [pid 3] [myuser] FTP response: Client "<client_ip>", "150 Here comes the directory listing."

The log always stops after "150 Here comes the directory listing.". I tried it several times.

And this is, what I see, when I use the ftp command on my terminal:

$ ftp -n 127.0.0.1

Connected to 127.0.0.1.
220 Welcome.
ftp> user myuser
331 Please specify the password.
Password:
230 Login successful.
ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
drwxr-xr-x    4 1000     1000         4096 Dec 28 13:27 dir1
226 Directory send OK.
ftp> cd dir1
250 Directory successfully changed.
ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
-rwxr-xr-x    1 1000     1000       469504 Dec 23 03:03 file_1
-rw-r--r--    1 1000     1000          186 Feb 19  2016 file_2
-rw-r--r--    1 1000     1000       121856 Dec 23 00:16 file_3
-rw-r--r--    1 1000     1000       118272 Feb 12  2016 file_4
-rw-r--r--    1 1000     1000        88232 Mar 22  2016 file_5
-rw-r--r--    1 1000     1000        64680 Mar 22  2016 file_6
-rw-r--r--    1 1000     1000       101032 Mar 22  2016 file_7
-rw-r--r--    1 1000     1000         6144 Mar 22  2016 file_8
-rw-r--r--    1 1000     1000       899584 Mar 22  2016 file_9
drwxrwxr-x   42 1000     1000         4096 Dec 28 11:38 dir2
226 Directory send OK.
ftp> cd dir2
250 Directory successfully changed.
ftp> pwd
257 "/dir1/dir2" is the current directory
ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
421 Service not available, remote server has closed connection

Thanks a lot for help.

Answer 1

I had the exact same problem, also on Arch Linux with vsftp 3.0.3 (pkg rel 3). It turned out the directory causing this behaviour had too many files in it (2,666). After removing most of them, listing over ftp started working again.

Weird, huh? 2,666 don't seem like too many. But I've really changed nothing else. vsftp settings are still the same and file system permissions are untouched. Also the file names didn't contain any strange characters (sequential numbers with a length of up to 21 chars).

Answer 2

I fixed the issue I has with directory listings failing with more than 10ish files (as described by Chistian Mund) by by adding this

seccomp_sandbox=NO

To /etc/vsftpd.conf

Source Arch Wiki