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Access Control,
Rootly Powers &
Controlling Processes
Prepared By
Prof. Bhushan Pawar
www.bhushanpawar.com
Prof.Bhushan Pawar
1

TRADITIONAL UNIX ACCESS CONTROL
• System’s design:
– Objects (e.g., files and processes) have
owners. Owners have broad (but not
necessarily unrestricted) control over their
objects.
– You own new objects that you create.
– The special user account called “root” can act
as the owner of any object.
– Only root can perform certain sensitive
administrative operations.
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Prof.Bhushan Pawar

File system access control
• In the traditional model, every file has both an owner
and a group, sometimes referred to as the “Group
owner.”
• The owner can set the permissions of the file.
• In particular, the owner can set them so restrictively
that no one else can access it.
• Groups are traditionally defined in the /etc/group
file, but these days group information is more
commonly stored on an NIS or LDAP server on the
network;
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Prof.Bhushan Pawar

Continue…
• The owner of a file gets to specify what the
group owners can do with it. This scheme
allows files to be shared among members of
the same project.
• The ownerships of a file can be determined
with
ls -l filename.
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Prof.Bhushan Pawar

Process ownership
• The owner of a process can send the process
signals and can also reduce the process’s
scheduling priority.
– The root account
– Setuid and Setgid execution
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Prof.Bhushan Pawar

The root account
• The root account is UNIX’s omnipotent (i.e having
unlimited power) administrative user. It’s also known
as the super user account, although the actual
username is “root”.
• Characteristic of the root account is its UID of 0 And
we cant modify the UID of it.
• Traditional UNIX allows the superuser (that is, any
process whose effective UID is 0) to perform any
valid operation on any file or process.
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Prof.Bhushan Pawar

Continue…
• Examples of restricted operations are
• Changing the root directory of a process with chroot
• Creating device files
• Setting the system clock
• Raising resource usage limits and process priorities
• Setting the system’s hostname
• Configuring network interfaces
• Opening privileged network ports (those numbered
below 1,024)
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Prof.Bhushan Pawar

Setuid and Setgid execution
• This mechanism lets developers and administrators
set up structured ways for unprivileged users to
perform privileged operations.
• When the kernel runs an executable file that has its
“setuid” or “setgid” permission bits set, it changes
the effective UID or GID of the resulting process to
the UID or GID of the file containing the program
image rather than the UID and GID of the user that
ran the command.
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Prof.Bhushan Pawar

MODERN ACCESS CONTROL
• From a security perspective, the root account
represents a potential single point of failure. If it’s
compromised, the integrity of the whole system is
violated. There is no limit to the damage an attacker
can inflict.
• The only way to subdivide the special privileges of
the root account is by writing setuid programs.
Unfortunately, as the Internet’s steady stream of
security updates demonstrates, it’s difficult to write
truly secure software.
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Prof.Bhushan Pawar

Continue…
• The security model isn’t strong enough for use on a
network. No computer to which an unprivileged user
has physical access can be trusted to accurately
represent the ownerships of the processes it’s
running.
• Many high-security environments enforce
conventions that simply can’t be implemented with
traditional UNIX security.
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Prof.Bhushan Pawar

Role-based access control
• Role-based access control, sometimes known as RBAC,
is a theoretical model formalized in 1992 by David
Ferraiolo and Rick Kuhn.
• The basic idea is to add a layer of indirection to access
control calculations. Instead of permissions being
assigned directly to users, they are assigned to
intermediate constructs known as “roles,” and roles in
turn are assigned to users.
• To make an access control decision, the access control
library enumerates the roles of the current user and
checks to see if any of those roles have the appropriate
permissions.
Prof.Bhushan Pawar
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PAM: Pluggable Authentication
Modules
• PAM is an authentication technology rather
than an access control technology. i.e rather
than addressing the question “Does user X
have permission to perform operation Y?”, it
helps answer the precursor question “How do
I know this is really user X?”
Prof.Bhushan Pawar
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Continue…
• In the past, user passwords were checked
against the /etc/shadow file at login time so
that an appropriate UID could be set for the
user’s shell or window system.
• Modern world of networks cryptography ,and
biometric identification devices, a more
flexible and open system is required.
Prof.Bhushan Pawar
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Continue…
• PAM is a wrapper for a variety of method-
specific authentication libraries. Administrator
specify the authentication methods he/she
want the system to use, along with the
appropriate contexts for each one. Programs
that want to authenticate a user simply call
the PAM system rather than implementing
their own forms of authentication.
Prof.Bhushan Pawar
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Kerberos: third-party
cryptographic authentication
• Kerberos deals with authentication rather
than access control But whereas PAM is an
authentication framework, Kerberos is a
specific authentication method.
• They’re generally used together, PAM being
the wrapper and Kerberos the actual
implementation.
Prof.Bhushan Pawar
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Continue…
• Kerberos uses a trusted third party (a server)
to perform authentication for an entire
network. Rather than authenticating yourself
to the machine you are using
Prof.Bhushan Pawar
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REAL-WORLD ACCESS CONTROL
• Most sites still use the traditional root
account for system administration.
• add-on tools such as sudo go a long way
toward bridging the gap between simplicity
and security.
Prof.Bhushan Pawar
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Choosing a root password
• The most important characteristic of a good
password is length. The root password should
be at least eight characters long.
• systems that use DES passwords with the help
of MD5 or Blowfish encryption for passwords
Prof.Bhushan Pawar
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Logging in to the root account
• We can log in directly to the root account and
work on the system. However, this turns out
to be a bad idea.
• Disadvantage is that the log-in-as-root
scenario leaves no record of who was really
doing the work.
• If several people have access to the root
account, you won’t be able to tell who used it
and when.
Prof.Bhushan Pawar
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su: substitute user identity
• Way to access the root account is to use the
su command.
• If invoked without arguments, su prompts for
the root password and then starts up a root
shell.
• Root privileges remain in effect until you
terminate the shell by typing <Control-D> or
the exit command.
Prof.Bhushan Pawar
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Continue…
• The su command can also substitute identities
other than root.
• If you know someone’s password, you can
access that person’s account directly by
executing su - username. The exact
implications of login mode vary by shell, but it
normally changes the number or identity of
the startup files that the shell reads.
Prof.Bhushan Pawar
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Continue…
• sudo takes as its argument a command line to be
executed as root.
• sudo consults the file /etc/sudoers, which lists
the people who are authorized to use sudo and
the commands they are allowed to run on each
host.
• sudo’s command logging can be subverted by
tricks such as shell escapes from within an
allowed program or by sudo sh and sudo su if
you allow them
Prof.Bhushan Pawar
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PSEUDO-USERS OTHER THAN ROOT
• Root is generally the only user that has special
status of the kernel, but several other pseudo-
users are defined by the system.
• You can identify these accounts by their low
UIDs, usually less than 100.
• UIDs under 10 are system accounts, and UIDs
between 10 and 100 are pseudo-users
associated with specific pieces of software.
Prof.Bhushan Pawar
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Any Question???
• If you having any doubt then you can ask me
question on
bhushan.pawar@mescoepune.org
Or
contact me on (+91)-7588318728
Prof.Bhushan Pawar
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Unit 5 access control,rootly powers & controlling processes

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