RBAC(5) Standards, Environments, and Macros RBAC(5)


NAME


rbac, RBAC - role-based access control

DESCRIPTION


The addition of role-based access control (RBAC) to the Solaris operating
environment gives developers the opportunity to deliver fine-grained
security in new and modified applications. RBAC is an alternative to the
all-or-nothing security model of traditional superuser-based systems.
With RBAC, an administrator can assign privileged functions to specific
user accounts (or special accounts called roles).


There are two ways to give applications privileges:

1. Administrators can assign special attributes such as setUID to
application binaries (executable files).

2. Administrators can assign special attributes such as setUID to
applications using execution profiles.


Special attribute assignment along with the theory behind RBAC is
discussed in detail in "Role Based Access Control" chapter of the System
Administration Guide: Security Services. This chapter describes what
authorizations are and how to code for them.

Authorizations


An authorization is a unique string that represents a user's right to
perform some operation or class of operations. Authorization definitions
are stored in a database called auth_attr(4). For programming
authorization checks, only the authorization name is significant.


Some typical values in an auth_attr database are shown below.

solaris.jobs.:::Cron and At Jobs::help=JobHeader.html
solaris.jobs.grant:::Delegate Cron & At \
Administration::help=JobsGrant.html
solaris.jobs.admin:::Manage All Jobs::help=AuthJobsAdmin.html
solaris.jobs.user:::Cron & At User::help=JobsUser.html


Authorization name strings ending with the grant suffix are special
authorizations that give a user the ability to delegate authorizations
with the same prefix and functional area to other users.

Creating Authorization Checks


To check authorizations, use the chkauthattr(3SECDB) library function,
which verifies whether or not a user has a given authorization. The
synopsis is:

int chkauthattr(const char *authname, const char *username);


The chkauthattr() function checks the policy.conf(4), user_attr(4), and
prof_attr(4) databases in order for a match to the given authorization.


If you are modifying existing code that tests for root UID, you should
find the test in the code and replace it with the chkauthattr() function.
A typical root UID check is shown in the first code segment below. An
authorization check replacing it is shown in the second code segment; it
uses the solaris.jobs.admin authorization and a variable called
real_login representing the user.

Example 1: Standard root check



ruid = getuid();

if ((eflag || lflag || rflag) && argc == 1) {
if ((pwp = getpwnam(*argv)) == NULL)
crabort(INVALIDUSER);

if (ruid != 0) {
if (pwp->pw_uid != ruid)
crabort(NOTROOT);
else
pp = getuser(ruid);
} else
pp = *argv++;
} else {


Example 2: Authorization check



ruid = getuid();
if ((pwp = getpwuid(ruid)) == NULL)
crabort(INVALIDUSER);

strcpy(real_login, pwp->pw_name);

if ((eflag || lflag || rflag) && argc == 1) {
if ((pwp = getpwnam(*argv)) == NULL)
crabort(INVALIDUSER);

if (!chkauthattr("solaris.jobs.admin", real_login)) {
if (pwp->pw_uid != ruid)
crabort(NOTROOT);
else
pp = getuser(ruid);
} else
pp = *argv++;
} else {


For new applications, find an appropriate location for the test and use
chkauthattr() as shown above. Typically the authorization check makes an
access decision based on the identity of the calling user to determine if
a privileged action (for example, a system call) should be taken on
behalf of that user.


Applications that perform a test to restrict who can perform their
security-relevant functionality are generally setuid to root. Programs
that were written prior to RBAC and that are only available to the root
user may not have such checks. In most cases, the kernel requires an
effective user ID of root to override policy enforcement. Therefore,
authorization checking is most useful in programs that are setuid to
root.


For instance, if you want to write a program that allows authorized users
to set the system date, the command must be run with an effective user ID
of root. Typically, this means that the file modes for the file would be
-rwsr-xr-x with root ownership.


Use caution, though, when making programs setuid to root. For example,
the effective UID should be set to the real UID as early as possible in
the program's initialization function. The effective UID can then be set
back to root after the authorization check is performed and before the
system call is made. On return from the system call, the effective UID
should be set back to the real UID again to adhere to the principle of
least privilege.


Another consideration is that LD_LIBRARY path is ignored for setuid
programs (see SECURITY section in ld.so.1(1)) and that shell scripts must
be modified to work properly when the effective and real UIDs are
different. For example, the -p flag in Bourne shell is required to avoid
resetting the effective UID back to the real UID.


Using an effective UID of root instead of the real UID requires extra
care when writing shell scripts. For example, many shell scripts check to
see if the user is root before executing their functionality. With RBAC,
these shell scripts may be running with the effective UID of root and
with a real UID of a user or role. Thus, the shell script should check
euid instead of uid. For example,

WHO=`id | cut -f1 -d" "`
if [ ! "$WHO" = "uid=0(root)" ]
then
echo "$PROG: ERROR: you must be super-user to run this script."
exit 1
fi


should be changed to

WHO=`/usr/xpg4/bin/id -n -u`
if [ ! "$WHO" = "root" ]
then
echo "$PROG: ERROR: you are not authorized to run this script."
exit 1
fi


Authorizations can be explicitly checked in shell scripts by checking the
output of the auths(1) utility. For example,

for auth in `auths | tr , " "` NOTFOUND
do
[ "$auth" = "solaris.date" ] && break # authorization found
done

if [ "$auth" != "solaris.date" ]
then
echo >&2 "$PROG: ERROR: you are not authorized to set the date"
exit 1
fi


SEE ALSO


ld.so.1(1), chkauthattr(3SECDB), auth_attr(4), policy.conf(4),
prof_attr(4), user_attr(4)


System Administration Guide: Security Services


July 15, 2003 RBAC(5)