Chapter 8
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Chapter 8. File System Security. File Protection Schemes. Login passwords Encryption File Access Privileges. Figure 8.1 The process of encryption and decryption. File Access Rights. Types of Users: Owner Group All/Other Types of Permissions: Read Write Execute Types of Files

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Chapter 8

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Chapter 8

Chapter 8

File System Security


File protection schemes

File Protection Schemes

  • Login passwords

  • Encryption

  • File Access Privileges


Figure 8 1 the process of encryption and decryption

Figure 8.1 The process of encryption and decryption


File access rights

File Access Rights

  • Types of Users:

    • Owner

    • Group

    • All/Other

  • Types of Permissions:

    • Read

    • Write

    • Execute

  • Types of Files

    • Directories

    • Other files


Table 8 1 summary of file permissions in linux

Table 8.1 Summary of File Permissions in LINUX


Directory permissions

Directory Permissions

  • read = list files in the directory

  • write = add new files to the directory

  • execute = access files in the directory


Determining file access rights

Determining File Access Rights


Table 8 2 permission values

Table 8.2 Permission Values


Table 8 3 permissions for access to courses labs and temp

Table 8.3 Permissions for Access to courses, labs, and temp


Changing the access rights

Changing the Access Rights

Purpose – to set/change permissions in files

  • chmod [options] octal-mode filelist

  • chmod [options] symbolic-mode filelist

    Options

  • -Rrecursively process subdirectories


Table 8 4 values for symbolic mode components

Table 8.4 Values for Symbolic Mode Components


Table 8 5 examples of the chmod commands and their purposes

Table 8.5 Examples of the chmod Commands and Their Purposes


Table 8 5 examples of the chmod commands and their purposes1

Table 8.5 Examples of the chmod Commands and Their Purposes


Figure 8 2 position of file type and access privilege bits for linux files as seen by ls l command

Figure 8.2  Position of file type and access privilege bits for LINUX files(as seen by “ls –l” command)


Figure 8 3 position of access privilege bits for linux files as specified in the chmod command

Figure 8.3  Position of access privilege bits for LINUX files as specified in the chmod command


Default file access rights

Default File Access Rights

  • umask is a bitmap which tells which permissions to deny by default on new files

  • 022 = 000 010 010 (deny write for g+o) rwx r-x r-x (new files permissions)

  • umask with no parameters returns the current mask value

  • umask newmask - sets new mask

  • umask command usually used in a startup file


Suid bit

SUID Bit

  • A special permission bit that allows executable files to run using the privileges of the owner of the files rather than the user of the file

  • Can be set using commands:

    chmodu+sfilelist

    chmod 4xxx filelist

  • Shows up in ls - l in place of the user x bit as an s if the file is executable - (rwsrwxrwx)

  • Very dangerous to use


Sgid bit

SGID Bit

  • A special permission bit that allows executable files to run using the privileges of the owner’s group rather than the user of the file

  • Set using the commands

    chmod g+s filelist

    chmod 2xxx filelist


Sticky bit

Sticky Bit

  • A special bit that can be used as follows:

  • For a file: it directs the operating system to keep the program in memory if possible after it finishes execution (Early versions of UNIX)

  • For a directory: it sets it up such that only the owner of the directory can delete (or rename) files from the directory, even if other users have write privilege (tmp)

  • Can be set using the chmod command using the options:chmod +t filelist

  • Shows up in “ls –l” as a t - (rwxrwxrwt)


  • Login