Hello everyone,

We have some chrooted sftp-only users on a CentOS release 6.6 server. The server had been logging their actions, but after recent updates the logs have stopped.

The server correctly logs non-chrooted users:

Sep 14 17:47:24 vsecure4 sshd[1981]: Accepted publickey for jcours from
192.168.10.166 port 42545 ssh2
Sep 14 17:47:24 vsecure4 sshd[1981]: pam_unix(sshd:session): session opened for user jcours by (uid=0)
Sep 14 17:47:24 vsecure4 sshd[1983]: subsystem request for sftp
Sep 14 17:47:24 vsecure4 internal-sftp[1984]: session opened for local user jcours from [192.168.10.166]
Sep 14 17:47:24 vsecure4 internal-sftp[1984]: opendir “/home/jcours”
Sep 14 17:47:24 vsecure4 internal-sftp[1984]: closedir “/home/jcours”
Sep 14 17:47:49 vsecure4 internal-sftp[1984]: session closed for local user jcours from [192.168.10.166]
Sep 14 17:47:19 vsecure4 sshd[1977]: pam_unix(sshd:session): session closed for user jcours

but log messages for chrooted users do not appear:

Sep 14 17:08:11 vsecure4 sshd[1730]: Accepted publickey for test-sftp-only from 192.168.10.166 port 41723 ssh2
Sep 14 17:08:11 vsecure4 sshd[1730]: pam_unix(sshd:session): session opened for user test-sftp-only by (uid=0)
Sep 14 17:08:11 vsecure4 sshd[1734]: subsystem request for sftp
Sep 14 17:08:22 vsecure4 sshd[1730]: pam_unix(sshd:session): session closed for user test-sftp-only

Notice that there are no “opendir” or “closedir” messages for the chrooted user, or anything else from the internal-sftp system, for that matter.

/etc/sshd_config contains these settings:

Subsystem sftp internal-sftp -f AUTHPRIV -l INFO

Match User test-sftp-only
ChrootDirectory /home/sftp/mcsosftp
ForceCommand internal-sftp
PasswordAuthentication no
AuthorizedKeysCommand /usr/local/bin/get_sftp_key

We’ve been setting up chrooted logging using this sequence:

sudo mkdir /home/sftp/mcsosftp/dev
sudo touch /home/sftp/mcsosftp/dev/log
sudo chattr +i /home/sftp/mcsosftp/dev
sudo mount –bind /dev/log /home/sftp/mcsosftp/dev/log

/etc/rsyslog.conf includes the standard stuff for authpriv:

# The authpriv file has restricted access.
authpriv.* /var/log/secure

I’ve tried forcing rsyslog.conf to listen to /dev/log:

# We should be listening here.
$SystemLogSocketName /dev/log

I’ve also tried removing the hard-mounted /home/sftp/mcsosftp/dev/log and instead using this in /etc/rsyslog.conf:

# For chrooted users, generally sftp-only users.
$AddUnixListenSocket /home/sftp/mcsosftp/dev/log

Neither approach seemed to help the problem, though rsyslogd does appear to be listening to the sockets:

$ sudo lsof -c rsyslogd | grep dev/log
lsof: WARNING: can’t stat() devtmpfs file system /home/sftp/dev/log
(deleted)
Output information may be incomplete.
rsyslogd 1963 root 0u unix 0xdc100040 0t0 15419 /dev/log
rsyslogd 1963 root 3u unix 0xdbd27dc0 0t0 15421
/home/sftp/mcsosftp/dev/log

and file identifies both as sockets:

$ file /dev/log
/dev/log: socket

$ sudo file /home/sftp/mcsosftp/dev/log
/home/sftp/mcsosftp/dev/log: socket

Here’s additional system info for the development server I’m using to debug the problem:

$ ls -l /dev/log
srw-rw-rw- 1 root root 0 Sep 14 17:43 /dev/log

$ sudo ls -l /home/sftp/mcsosftp/dev/log
srw-rw-rw- 1 root root 0 Sep 14 17:43 /home/sftp/mcsosftp/dev/log

$ ls -l /dev | grep log
srw-rw-rw- 1 root root 0 Sep 14 17:43 log
crw-rw—- 1 root root 10, 227 Sep 14 15:23 mcelog

$ sudo ls -l /home/sftp/mcsosftp/dev | grep log
srw-rw-rw- 1 root root 0 Sep 14 17:43 log

$ cat /etc/redhat-release
CentOS release 6.6 (Final)

$ sestatus
SELinux status: disabled

$ grep test-sftp-only /etc/passwd
test-sftp-only:x:507:507:Test SFTP
Only:/home/sftp/mcsosftp:/sbin/nologin

$ sudo yum list installed | egrep -E ‘rsyslog|ssh|sftp’
libssh2.i686 1.4.2-1.el6_6.1 @updates
openssh.i686 5.3p1-104.el6_6.1 @updates
openssh-clients.i686 5.3p1-104.el6_6.1 @updates
openssh-server.i686 5.3p1-104.el6_6.1 @updates
rsyslog.i686 5.8.10-10.el6_6 @updates
vsftpd.i686 2.2.2-14.el6 @base

Corresponding packages on the production server showing the same problem:

$ sudo yum list installed | egrep -E ‘rsyslog|ssh|sftp’
libssh2.x86_64 1.4.2-1.el6_6.1
@system-updates
openssh.x86_64 5.3p1-112.el6_7
@system-updates
openssh-clients.x86_64 5.3p1-112.el6_7
@system-updates
openssh-server.x86_64 5.3p1-112.el6_7
@system-updates
rsyslog.x86_64 5.8.10-10.el6_6
@system-updates
rsyslog-gnutls.x86_64 5.8.10-10.el6_6
@system-updates

Does anyone have any ideas what the problem could be or how to diagnose it?

Thanks very much in advance, Jeff