Saturday, November 27, 2004

AntiVirus on GNU/Linux?

There has been a fact that GNU/Linux is not vulnerable to Virus, Worms, or their variants, but in reality, GNU/Linux is being used as the main web server, proxy server, mail server, firewall, file server that it's client is Windows-based and therefore, it should hold up as many virus, worms, or other threats that will penetrate to the internal networks. Here is a good article about consideration using Antivirus on GNU/Linux :

Should I get anti-virus software for my Linux box?

The problem with answering this question is that those asking it know only OSes where viruses, trojan-horse programs, worms, nasty Javascripts, ActiveX controls with destructive payloads, and ordinary misbehaved applications are a constant threat to their computing. Therefore, they refuse to believe Linux could be different, no matter what they hear.

And yet it is.

Here's the short version of the answer: No. If you simply never run untrusted executables while logged in as the root user (or equivalent), all the "virus checkers" in the world will be at best superfluous; at worst, downright harmful. "Hostile" executables (including viruses) are almost unfindable in the Linux world — and no real threat to it — because they lack root-user authority, and because Linux admins are seldom stupid enough to run untrusted executables as root, and because Linux users' sources for privileged executables enjoy paranoid-grade scrutiny (such that any unauthorised changes would be detected and remedied).

Here's the long version: Still no. Any program on a Linux box, viruses included, can only do what the user who ran it can do. Real users aren't allowed to hurt the system (only the root user can), so neither can programs they run.

Because of the distinction between privileged (root-run) processes and user-owned processes, a "hostile" executable that a non-root user receives (or creates) and then executes (runs) cannot "infect" or otherwise manipulate the system as a whole. Just as you can delete only your own files (i.e., those you have "write" permission to), executables you run cannot affect other users' (or root's) files. Therefore, although you can create (or retrieve), and then run, a virus, worm, trojan horse, etc., it can't do much. Unless you do so as "root". Which it's simple to avoid doing.

The first "virus" (arguably, actually a trojan or worm) for Linux was named "Bliss", created in September 1996 as a proof of concept. If a user executes an infected executable, the viral code appends itself to all executables for which the user has write permission. But thereafter, it can't go anywhere else or do anything else — and cannot take over (infect) the local machine (or any other): It lacks permission to do so. Nor can the other Linux/Unix viruses / worms / trojan horses thus far known. And claims of "Bliss" infections outside deliberate lab-only deployment by virus researchers are, in point of fact, considered suspect. New Linux viruses (such as Simile.D) emerge continually, too. But guess what? They don't go anywhere, either.

Most people asking this question have no experience with true multi-user systems built around a pervasive, ground-up security model. On their systems, any process the user executes, directly or indirectly, can modify, destroy, or manipulate anything on the system. This is true to a degree even on MS-Windows NT/XP, which tries to be fully multiuser as Unixes are, but has numerous fundamental security flaws.

By contrast, on Linux (or any other Unix), your processes cannot harm the machine (or damage other users' files) — because you yourself cannot.

Thus, even a Linux user who deliberately wants to activate a Linux virus (trojan horse, worm, or other program designed to do mischief) will have extreme difficulty getting it to circulate. If you're a programmer, try and see. Viruses aren't difficult to write on Linux: Write one, run it (as a non-root user), and watch it bollix your files. But nobody else's.

-- read the full article --

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