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secure /tmp on servers

Check if /tmp is already secure. Some servers do not use a /tmp partition while others do.
-----command-----
df -h |grep tmp
-----command-----

If that displays nothing then go below to create a tmp partition. If you do have a tmp partition you need to see if it mounted with noexec.
-----command-----
cat /etc/fstab |grep tmp
-----command-----

If there is a line that includes /tmp and noexec then it is already mounted as non-executable. If not follow the instructions below to create one without having to physically format your disk. Idealy you would make a real partition when the disk was originally formated, that being said I have not had any trouble create a /tmp partition using the following method.

Create a ~800Mb partition
-----command-----
cd /dev/; dd if=/dev/zero of=tmpMnt bs=1024 count=800000
-----command-----

Format the partion
-----command-----
mkfs.ext2 /dev/tmpMnt
-----command-----
When it asks about not being a block special device press Y

Make a backup of the old data
-----command-----
cp -Rp /tmp /tmp_backup
-----command-----

Mount the temp filesystem
-----command-----
mount -o loop,noexec,nosuid,rw /dev/tmpMnt /tmp
-----command-----

Set the permissions
-----command-----
chmod 0777 /tmp
-----command-----

Copy the old files back
-----command-----
cp -Rp /tmp_backup/* /tmp/
-----command-----

Once you do that go ahead and restart mysql and make sure it works ok. We do this because mysql places the mysql.sock in /tmp which neeeds to be moved. If not it migth have trouble starting. If it does you can add this line to the bottom of the /etc/fstab to automatically have it mounted:

Open the file in pico:
-----command-----
pico -w /etc/fstab
-----command-----

Now add this single line at the bottom:

/dev/tmpMnt /tmp ext2 loop,noexec,nosuid,rw 0 0

While we are at it we are going to secure /dev/shm. Look for the mount line for /dev/shm and change it to the following:
none /dev/shm tmpfs noexec,nosuid 0 0

Umount and remount /dev/shm for the changes to take effect.
-----command-----
umount /dev/shm
mount /dev/shm
-----command-----

Delete the old /var/tmp and create a link to /tmp
-----command-----
rm -rf /var/tmp/
ln -s /tmp/ /var/
-----command-----

If everything still works fine,  delete the /tmp_backup directory.
-----command-----
rm -rf /tmp_backup
-----command-----

Your /tmp, /var/tmp, and /dev/shm are now mounted in a way that no program can be directly run from these directories.


Author: admin -  Date: 12 Jan 2020 07:31
Category: linux -  Visits: 103

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