PowerScale OneFS: Error Received After Upgrade "500 OOPS: Vsftpd: Refuses to Run with Writable Root Inside Chroot"

FTP user login fails with:

500 OOPS: vsftpd: refusing to run with writable root inside chroot()

The issue occurs after upgrading OneFS to a version containing upgraded vsftpd:

• 8.2.2_GA-RUP_2023-06 and later
• 9.1.0.29 and later
• 9.2.1.23 and later
• 9.4.0.14 and later
• 9.5.0.4 and later
• 9.6.0.0 and later

For example, the vsftpd pkg is updated from vsftpd-ssl-2.3.4vsftpd-ssl-3.0.5.

More information is available on the vsftpd official home page at https://security.appspot.com/vsftpd/Changelog.txt 

- Add stronger checks for the configuration error of running with a writeable root directory inside a chroot(). This may bite people who carelessly turned on chroot_local_user but such is life.
- Add new config setting "allow_writeable_chroot" to help people in a bit of a spot with the v2.3.5 defensive change. Only applies to non-anonymous.

The issue is that the FTP user's root directory is writable. The chroot limit is used, which is not allowed in the recent update. The chroot directory that users are locked to must not be writable.

• Option 1: Remove write permissions on the user's root directory.

#chmod a-w /home/user

• Option 2: Work around the stronger checks by adding the configuration settings below into the vsftpd global configuration file or individual user configuration file:

allow_writeable_chroot=YES

On the OneFS cluster, it is recommended to make a copy of the vsftpd configuration to /ifs/data/Isilon_Support/.
For example:

# cp -av /etc/mcp/templates/vsftpd.conf  /ifs/data/Isilon_Support/vsftpd.conf.bak

Then, using the VI editor, add the following line to /etc/mcp/templates/vsftpd.conf "

allow_writeable_chroot=YES"

Another option instead of using the VI editor is to use the echo command to append a line to that same file: 

# echo "allow_writeable_chroot=YES"  >>  /etc/mcp/templates/vsftpd.conf

Wait for a few seconds, then check that the file gets updated to all nodes and that the file md5 checksum is consistent.

# isi_for_array -s md5 /etc/mcp/templates/vsftpd.conf

Here is a quick reproduction of the issue and the steps to fix it:

1. Log in to a PowerScale cluster running OneFS 9.4.0.14. Below is the FTP user home directory:

test2-fxq5rm3-1# ls -ld /ifs/home/warmsvcisiftp
drwx------     2 warmsvcisiftp  Isilon Users  264 Jun 13 02:50 /ifs/home/warmsvcisiftp

2. FTP user login fails with the error message:

test2-fxq5rm3-1# ftp localhost
Trying 127.0.0.1:21 ...
Connected to localhost.
220-PowerScale OneFS 9.4.0.14
220
Name (localhost:root): warmsvcisiftp
331 Please specify the password.
Password:
500 OOPS: vsftpd: refusing to run with writable root inside chroot()
ftp: Login failed
ftp>

3. There are two options to address this issue depending on your workflow and concerns:

• Option 1:  Remove the write permissions for the user's root directory:

test2-fxq5rm3-1# chmod a-w /ifs/home/warmsvcisiftp
test2-fxq5rm3-1# ls -ld /ifs/home/warmsvcisiftp
dr-x------     2 warmsvcisiftp  Isilon Users  264 Jun 13 02:50 /ifs/home/warmsvcisiftp

test2-fxq5rm3-1# ftp localhost
Trying 127.0.0.1:21 ...
Connected to localhost.
220-PowerScale OneFS 9.4.0.14
220
Name (localhost:root): warmsvcisiftp
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> bye
221 Goodbye.

• Option 2: Work around the security check:

test2-fxq5rm3-1# chmod u+w /ifs/home/warmsvcisiftp
test2-fxq5rm3-1# ls -ld /ifs/home/warmsvcisiftp
drwx------     2 warmsvcisiftp  Isilon Users  264 Jun 13 02:50 /ifs/home/warmsvcisiftp
test2-fxq5rm3-1# echo "allow_writeable_chroot=YES" >> /etc/mcp/templates/vsftpd.conf
test2-fxq5rm3-1# isi_for_array -s md5 /etc/mcp/templates/vsftpd.conf
test2-fxq5rm3-1: MD5 (/etc/mcp/templates/vsftpd.conf) = 4920beaff65c3bfa09bd18582c2fbcf8
test2-fxq5rm3-2: MD5 (/etc/mcp/templates/vsftpd.conf) = 4920beaff65c3bfa09bd18582c2fbcf8
test2-fxq5rm3-3: MD5 (/etc/mcp/templates/vsftpd.conf) = 4920beaff65c3bfa09bd18582c2fbcf8
test2-fxq5rm3-1# ftp localhost
Trying 127.0.0.1:21 ...
Connected to localhost.
220-PowerScale OneFS 9.4.0.14
220
Name (localhost:root): warmsvcisiftp
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> bye
221 Goodbye.

• Dell article Isilon: OneFS 8.X and Later: How to lock (chroot (change root) jail) FTP users into a specific directory
• ArchLinux document, Very Secure FTP Daemon