Increase NFS Client Mount Point Security For a Web-Server noexec, nosuid, nodev Options
I
am using NFS server version 4.x on a CentOS/RHEL based system. I’m mounting my shared /var/www/ directory on five Apache based nodes using the following syntax:
mount -t nfs4 -o rw,intr,hard,proto=tcp rocknas02:/httproot/www /var/www/
I noticed that due to bug in my app user can sometime upload executable or other device files to get out of chrooted Apache server. How can I prevent such security issues on a CentOS or RHEL based NFS client and sever setup?
First, you need to fix your application. Next, you can pass the following three options to mount command to increase overall security on Apache/Nginx/Lighttpd nfs based client:
noexec – Prevents execution of binaries on mounted file systems. This prevents remote users from executing unwanted binaries on your system.
nosuid – Disables set-user-identifier or set-group-identifier bits. This prevents remote users from gaining higher privileges by running a setuid program.
nodev – Prevents character and block special devices from being defined, or if they exist, from being used as character and block special devices. This prevents remote users from getting out of chrooted server jails.
Modify your mount command as follows:
# mount -t nfs4 -o rw,intr,hard,proto=tcp,nodev,noexec,nosuid rocknas02:/httproot/www /var/www/
OR attempt to remount an already-mounted nfsv4.0 filesystem:
# mount -t nfs4 -o remount,rw,intr,hard,proto=tcp,nodev,noexec,nosuid rocknas02:/httproot/www /var/www/
Test it
To verify new settings, enter:
# mount
# mount | grep rocknas02
Sample outputs:
rocknas02:/httproot/www on /var/www type nfs4 (rw,noexec,nosuid,nodev,sync,intr,hard,proto=tcp,addr=192.168.1.10,clientaddr=192.168.1.100)
Copy /bin/ls to rocknas02:/httproot/www i.e. type the following on your nfsv4.0 server called rocknas02
# cp /bin/ls /httproot/www
On client, type:
cd /var/www
run /bin/ls
ls -l
# Run uploaded ls
./ls
Sample outputs:
Fig. 01: Running ls command on nfs client
Updating /etc/fstab is left as an exercise for the reader.
Mount the filesystem read-only
If possible mount the filesystem in read-only mode. Modify your mount command as follows:
# mount -t nfs4 -o ro,intr,hard,proto=tcp,nodev,noexec,nosuid rocknas02:/httproot/www /var/www/
OR attempt to remount an already-mounted nfsv4.0 filesystem:
# mount -t nfs4 -o remount,ro,intr,hard,proto=tcp,nodev,noexec,nosuid rocknas02:/httproot/www /var/www/
Recommend file/directory permission for Apache
I suggest the following schema:
Run Apache as apache user and group
You must run httpd as root initially and it will switch to apache user and group:
# egrep -i ^(User|Group) /etc/httpd/conf/httpd.conf
Sample outputs:
User apache
Group apache
NFS server file/directory permission for /var/www/
Create a user called www-files using useradd command:
# useradd -d /var/www -M -s /sbin/nologin www-files
Make sure you lock www-files account using passwd command:
# passwd -l www-files
Change file owner and group to www-files for /var/www directory use the following passwd command:
# chown -R www-files:www-files /var/www/
Finally changes the file mode bits of each given file and directory according to mode:
By default all files & dirs permissions are set to read-only ###
chmod -R 0444 /var/www
Allow, apache/nginx/lighttpd to serve files from directory by settings others to x bit ###
find /var/www -type d -print0 | xargs -0 -I {} chmod 0445 {}
Optional certain directory may need additional permissions such as /var/www/uploads ###
#chmod 0777 -R /var/www/uploads
Use ls -l command to verify file permissions:
# cd /var/www
# ls -l
Sample outputs:
total 32
-r–r–r–. 1 www-files www-files 606 Dec 21 2011 best_resources.php
-r–r–r–. 1 www-files www-files 1068 Sep 4 2011 cdn_info_linux_unix_setup.php
dr–r–r-x. 2 www-files www-files 4096 Aug 5 2012 data
….
…
…
-r–r–r–. 1 www-files www-files 1550 Jun 22 2012 service-per-vm-guide.php
See also
How to configure php to deny file uploads.
This entry is 15 of 15 in the Linux / UNIX NFS File Server Tutorial series. Keep reading the rest of the series:
CentOS / Redhat: Setup NFS v4.0 File Server
Debian / Ubuntu Linux: Setup NFSv4 File Server
Mac Os X: Mount NFS Share / Set an NFS Client
RHEL: How Do I Start and Stop NFS Service?
How To Restart Linux NFS Server Properly When Network Become Unavailable
Linux Iptables Allow NFS Clients to Access the NFS Server
Debian / Ubuntu Linux Disable / Remove All NFS Services
Linux: Tune NFS Performance
Mount NFS file system over a slow and busy network
Linux Track NFS Directory / Disk I/O Stats
Linux Disable / Remove All NFS Services
Linux: NFS4 mount Error reason given by server: No such file or directory
Linux NFS Mount: wrong fs type, bad option, bad superblock on fs2:/data3 Error And Solution
CentOS / RHEL CacheFS: Speed Up Network File System (NFS) File Access
Increase NFS Client Mount Point Security