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59 lines
2.5 KiB
59 lines
2.5 KiB
Overview
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--------
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As of Linux 2.2.0, the power of the superuser has been partitioned
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into a set of discrete capabilities (in other places, these
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capabilities are know as privileges).
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The contents of the libcap package are a library and a number of
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simple programs that are intended to show how an application/daemon
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can be protected (with wrappers) or rewritten to take advantage of
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this fine grained approach to constraining the danger to your system
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from programs running as 'root'.
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Notes on securing your system
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-----------------------------
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Adopting a role approach to system security:
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changing all of the system binaries and directories to be owned by
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some user that cannot log on. You might like to create a user with
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the name 'system' who's account is locked with a '*' password. This
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user can be made the owner of all of the system directories on your
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system and critical system binaries too.
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Why is this a good idea? In a simple case, the CAP_FUSER capabilty is
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required for the superuser to delete files owned by a non-root user in
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a 'sticky-bit' protected non-root owned directory. Thus, the sticky
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bit can help you protect the /lib/ directory from an compromized
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daemon where the directory and the files it contains are owned by the
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system user. It can be protected by using a wrapper like execcap to
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ensure that the daemon is not running with the CAP_FUSER capability...
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Limiting the damage:
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If your daemon only needs to be setuid-root in order to bind to a low
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numbered port. You should restrict it to only having access to the
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CAP_NET_BIND_SERVICE capability. Coupled with not having any files on
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the system owned by root, it becomes significantly harder for such a
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daemon to damage your system.
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Note, you should think of this kind of trick as making things harder
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for a potential attacker to exploit a hole in a daemon of this
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type. Being able to bind to any privileged port is still a formidable
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privilege and can lead to difficult but 'interesting' man in the
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middle attacks -- hijack the telnet port for example and masquerade as
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the login program... Collecting passwords for another day.
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The /proc/ filesystem:
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This Linux-specific directory tree holds most of the state of the
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system in a form that can sometimes be manipulated by file
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read/writes. Take care to ensure that the filesystem is not mounted
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with uid=0, since root (with no capabilities) would still be able to
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read sensitive files in the /proc/ tree - kcore for example.
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[Patch is available for 2.2.1 - I just wrote it!]
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