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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 737
706
SECURITY
CHAP. 9
PROBLEMS
1.
Confidentiality, integrity, and availability are three components of security.
Describe
an application that integrity and availability but not confidentiality, an application that
requires confidentiality and integrity but not (high) availability, and an application that
requires confidentiality, integrity, and availability
2.
One of the techniques to build a secure operating system is to minimize the size of
TCB. Which of the following functions needs to be implemented inside the TCB and
which can be implemented outside TCB: (a) Process context switch; (b) Read a file
from disk; (c) Add more swapping space; (d) Listen to music; (e) Get the GPS coordi-
nates of a smartphone.
3.
What is a covert channel? What is the basic requirement for a covert channel to exist?
4.
In a full access-control matrix, the rows are for domains and the columns are for ob-
jects. What happens if some object is needed in two domains?
5.
Suppose that a system has 5000 objects and 100 domains at some time. 1% of the ob-
jects are accessible (some combination of
r
,
w
and
x
) in all domains, 10% are ac-
cessible in two domains, and the remaining 89% are accessible in only one domain.
Suppose one unit of space is required to store an access right (some combination of
r
,
w
,
x
), object ID, or a domain ID.
How much space is needed to store the full protec-
tion matrix, protection matrix as ACL, and protection matrix as capability list?
6.
Explain which implementation of the protection matrix is more suitable for the follow-
ing operations:
(a) Granting read access to a file for all users.
(b) Revoking write access to a file from all users.
(c) Granting write access to a file to John, Lisa, Christie, and Jeff.
(d) Revoking execute access to a file from Jana, Mike, Molly, and Shane.
7.
Two different protection mechanisms that we have discussed are capabilities and ac-
cess-control lists. For each of the following protection problems, tell which of these
mechanisms can be used.
(a) Ken wants his files readable by everyone except his office mate.
(b) Mitch and Steve want to share some secret files.
(c) Linda wants some of her files to be public.
8.
Represent the ownerships and permissions shown in this UNIX directory listing as a
protection matrix.
(
Note
:
asw
is a member of two groups:
users
and
devel
;
gmw
is a
member only of
users
.) Treat each of the two users and two groups as a domain, so
that the matrix has four rows (one per domain) and four columns (one per file).
– rw– r– – r– –
2
gmw
users
908
May 26 16:45
PPP– Notes
–rwx r–x r–x
1
asw
devel
432
May 13 12:35
prog1
– rw– rw– – – –
1
asw
users
50094
May 30 17:51
project.t
– rw– r– – – – –
1
asw
devel
13124
May 31 14:30
splash.gif
9.
Express the permissions shown in the directory listing of the previous problem as ac-
cess-control lists.
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