[ubuntu-hardened] Polyinstantiate /tmp, /var/tmp and user home folders.

daniel curtis sidetripping at gmail.com
Sun Feb 21 16:07:07 UTC 2016


Today I would like to ask a question about Polyinstantiate and PAM to
improve system security. Polyinstantiation of some world-writable
directories (e.g. /tmp, /var/tmp) could prevent multiple type of attacks,
such as: attacks by one user on another user, attacks by a user on a daemon
or attacks by a non-root daemon on a user to name a few.

Using this type of protection is pretty simple. To enable this feature user
have to edit '/etc/security/namespace.conf' file, uncomment at least three
lines and add one entry to the '/etc/pam.d/login' file. Of course
'/tmp-inst/' and '/var/tmp/tmp-inst/' directories must be created e.g. via
'mkdir' command.

There are an interesting articles/descriptions about Polyinstantiation of
directories (please note, despite title, that this feature also provides
benefits for non-SE Linux systems):


(Especially see: "Other Solutions", "Non-SE Linux Requirements for Shared
Directories"). There are two more interesting articles. One from Fedora
Linux[1] and second from an IBM[2].

According to all above, I would like to know your opinions about this
security feature. It is worth to implement etc.? What do you think about

Best regards.
[1] https://fedoraproject.org/wiki/Security_Features_Matrix (see
"Polyinstantiate /tmp, /var/tmp and user home folders")
[2] https://www.ibm.com/developerworks/library/l-polyinstantiation/
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