Object Security
Operating Systems 1
Object Security
COMP755 Advanced Operating
Systems
Object Permissions
• Operating systems must determine if a
user has permission to perform an action
upon an object.
• The objects that we are usually concerned
with are files and printers.
Access Control
• The definition of access rights can be
defined for a user or an object.
•Capabilities specify what a user can do.
•Access Control Lists (ACL) are created
for each object and specify who can
perform what action.
Access Matrix
• Row are capabilities
• Columns are access control lists
list /
write
print /
manage
read /
execute
read /
write
userB
listprintread /
execute
readuserA
/dirPrt1FileYFileX
Complex Security Access
• Imagine you have a file of sensitive
information. You want users to be able to
run your program to add data to the file but
you don’t want users to be able to read the
file.
• Imagine you are a manager going on
leave. You want to give your assistant
certain privileges while you are gone. You
don’t want them to be able to do anything
and you want to rescind privileges on your
return.
Unix File Security
• Unix files use Access Control Lists.
• Each file has 9 bits defining the access
rights
user group world
RWX RWX RWX
• Rights can be expressed as a three digit
octal number
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