Lecture Slides on File Systems - Operating Systems | CSCI 1670, Papers of Operating Systems

Download Lecture Slides on File Systems - Operating Systems | CSCI 1670 and more Papers Operating Systems in PDF only on Docsity! File Systems (The End!) cs 167 XxIV-1 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Flash Memory * Two technologies —nor - byte addressable —nand - page addressable + Writing — newly “erased” block is all ones — “programming” changes some ones to zeroes - per byte in nor; per page in nand (multiple pages/block) - to change zeroes to ones, must erase entire block - can erase no more than ~100k times/block cs 167 XxIV-2 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Flash with FTL * Which file system? — FAT32 (sort of like S5FS, but from Microsoft) —NTFS —FFS — Ext3 cs 167 XXIV-5. Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Flash without FTL * Known as memory technology device (MTD) — software wear-leveling — perhaps other tricks cs 167 XXIV-6 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  JFFS and JFFS2 ¢ Journaling flash file system — log-based: no journal! - each log entry contains inode info and some data - garbage collection copies info out of partially obsoleted blocks, allowing block to be erased - complete index of inodes kept in RAM - entire file system must be read when mounted cs 167 XXIV-7 Copyright © 2008 Thomas W. Doeppner. Al rights reserved. See http://sourceware.org/jffs2/jffs2-html/jffs2-html.html for descriptions of JFFS and JFFS2.  Security (Part 1) cs 167 XXIV=10 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Security + Framework — authentication — access control ¢ Breaking and entering — prevention cs 167 XXIV=14 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Concerns + Authentication — who are you? + Access control — what are you allowed to do? + Availability —can others keep you out? cs 167 XXIV=12, Copyright © 2008 Thomas W. Doeppner. Al rights reserved. Systems that employ just one-way functions to protect their passwords are vulnerable to dictionary attacks. Unix uses “salt” as a means to foil dictionary attacks, though it’s probably not of tremendous use anymore. Counter Counter Attacks + Don’t allow common access to password images —/etc/passwd contains everything but password images and is readable by all — /etc/shadow contains password images + Use better passwords — “w7%3ngibwy6” rather than “fido” + Use strong cryptography and smart cards — combined with PINs + Use biometrics cs 167 XXIV-17 Copyright © 2008 Thomas W. Doeppner. Al rights reserved. We now turn our attention to hacking. Though we don’t provide a whole lot of detail in our description. All the details (and excellent working code) are provided at numerous sites on the Web. . Trap doors Trojan horses Attacks Viruses and worms Exploit bugs Exploit features cs 167 XXIV-21 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Trap Doors * You supply a CD driver * ioctl (cd_file_descriptor, 0x5309) — standard command to eject the CD * ioctl (cd_file_descriptor, 0xe311) — second argument is passed to your driver — on receipt, your driver sets UID of current process to zero cs 167 XXIV-22 Copyright © 2008 Thomas W. Doeppner. Al rights reserved. On Unix systems, “superuser” has a UID of zero.  Trojan Horses + Free software!!! — upgrades your DVD-ROM into a DVD-RW!! cs 167 XXIV-25 ‘Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  Viruses and Worms * Virus: an “infection” of a program that replicates itself + Worm: a standalone program that actively replicates itself cs 167 XXIV-26 ‘Copyright © 2008 Thomas W. Doeppner. Al  How to Write a Virus (1) Program (date) Virus (/bin/rm —rf /) cs 167 XXIV-27 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.  How to Write a Virus (4) ES Program (date; if (day == Tuesday) /bin/rm —rf /) cs 167 XXIV-30 Copyright © 2008 Thomas W. Doeppner. Al  How to Write a Virus (5) Program (date; if (day == Tuesday) /bin/rm -rf /; infect others) cs 167 XXIV-34 Copyright © 2008 Thomas W. Doeppner. All rights reserve.  Further Issues + Make program appear unchanged — don’t change creation date — don’t change size + How to infect others — email —web — direct attack — etc. cs 167 XXIV-32 Copyright © 2008 Thomas W. Doeppner. Al rights reserved.