Unix

10 Pages 2480 Words

Following is all the information that you need to understand the workings of
the UNIX operating system (Berkley 4.2).

Patched together by The War


On the security side of UNIX:
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On the Security of UNIX Dennis M. Ritchie Recently there has been much interest
in the security aspects of operating systems and software. At issue is the
ability to prevent undesired disclosure of information, destruction of
information, and harm to the functioning of the system. This paper discusses
the degree of security which can be provided under the system and offers a
number of hints on how to improve security. The first fact to face is that was
not developed with security, in any realistic sense, in mind; this fact alone
guarantees a vast number of holes. (Actually the same statement can be made
with respect to most systems.) The area of security in which is theoretically
weakest is in protecting against crashing or at least crippling the operation
of the system.
The problem here is not mainly in uncritical acceptance of bad parameters
to system calls there may be bugs in this area, but none are known- but rather
in lack of checks for excessive consumption of resources. Most notably, there
is no limit on the amount of disk storage used, either in total space allocated
or in the number of files or directories. Here is a particularly ghastly shell
sequence guaranteed to stop the system:

while :; do
mkdir x
cd x
done

Ether a panic will occur because all the i-nodes on the device are used up,
or all the disk blocks will be consumed, thus preventing anyone from
writing files on the device. In this version of the system, users are
prevented from creating more than a set number of processes simultaneously, so
unless users are in collusion it is unlikely that any one can stop the
system altogether. However, creation of 20 or so CPU or disk-bound jobs
l...