Shell Alias May Be Dangerous

 Computing, Linux  No Responses »
Jul 132022
 

Not all shell aliases of course, but some. I’ve just seen a youtube video that suggested creating a shell alias to run rmtrash when rm is invoked :-

alias rm='rmtrash'

Seems sensible enough doesn’t it? This is in fact the classic example of how dangerous shell aliases can be, although the classic example was to turn on “-i” :-

alias rm='rm -i'

The problem is that you get used to “rm” being safe – either it asks before it removes files (“-i”) or it safely preserves what is deleted in the Trash folder. But what happens when the alias doesn’t get created? Perhaps you have a broken .zshrc and Zsh stops interpreting before the alias is declared. Or you’ve logged on to a remote server that doesn’t have your .zshrc installed as yet?

All of a sudden you are running the unadulterated rm command – deleting files without being asked, or preserving them in the Trash folder. See the danger now?

It is better not to replace standard commands but create a new ‘command’ :-

alias del="rmtrash"

Perhaps you regard this as being excessively risk averse – fair enough. But just don’t say you weren’t warned – and I’ve encountered missing aliases every year over the last 30-odd years I’ve been using Linux and Unix.

The Bare Family

Reducing Risk in System Management

 Computing  No Responses »
Oct 082019
 

I was reminded of something recently when someone was using a gooey; they hadn’t made any changes, but clicked “Ok” after reviewing something. A bug in the gooey resulted in a whole bunch of DNS CNAMEs being removed.

The fault is of course with the gooey for having a silly bug, but it was also a reminder to reduce risk whenever you have root (or equivalent).

  1. The “Ok” in a gooey should be read as “Please make the changes I have asked for”; if you are not intentionally making changes, why click on it?
  2. One of the reasons I switched to zsh was that I’d heard of accidents involving wildcards, so I wanted the feature that expanded wildcards within the shell before activating the command.
  3. If you are looking at a configuration file, why are you using an editor? Use view rather than vi, and if you are in vi quit (“:q!”) rather than save and exit (“ZZ”).
  4. If you have an account with special rights , don’t browse the Internet with it. You should have two accounts – one for ordinary stuff and one used just when you need additional rights. That’s two long and strong passwords to remember; life is hard; get used to it.

But this is more than just a few tips for reducing risk; it’s about an attitude that goes beyond simply being careful and towards designing your work flow in ways that reduces risk.

Old Metal 3

Manually Setting IP Addresses – Use CIDR Format!

 Computing, Working Notes  No Responses »
Feb 242019
 

Normally when you set an IP address manually on an interface you do not get a whole lot of choice of how it is done – very often you have to specify the IP address itself and a network mask. The addresses and masks are almost always specified as “dotted quads” (10.0.0.1) rather than the real address in binary or decimal (167772161).

The network mask specifies what parts of the IP address are the network address and which are the host address – to determine whether a destination needs to go via a gateway or is on the local network. This is expressed as a bitmask like 255.255.255.0. Having said that, rarely some devices (Cisco routers in the dustier parts of their code) require the reverse – 0.0.0.255.

An alternative approach is to use the CIDR format to specify both the IP address of the device and the size of the network – 10.2.9.21/24. This is used (at least) on Palo Alto Networks firewalls and is probably the simplest way of configuring a network address I have come across.

Having configured hundreds of devices with static addresses … and helped solve oodles of network configuration issues, I feel that the CIDR format method is likely to be far less error prone.

If you do need to set a netmask, use ipcalc to check what it is (and use it to cut&paste rather than risk typos) :-

✓ mike@pica» ipcalc 10.2.9.21/24 
Address:   10.2.9.21            00001010.00000010.00001001. 00010101
Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
=>
Network:   10.2.9.0/24          00001010.00000010.00001001. 00000000
HostMin:   10.2.9.1             00001010.00000010.00001001. 00000001
HostMax:   10.2.9.254           00001010.00000010.00001001. 11111110
Broadcast: 10.2.9.255           00001010.00000010.00001001. 11111111
Hosts/Net: 254                   Class A, Private Internet
Through The Gateway

Not Victim Blaming. Risk Reduction.

 General, Security  No Responses »
Jan 302015
 

There's a game called "victim blaming" which is where people decide the victim of a crime is somehow partially or wholely respomsible – the old "if she hadn't worn such a short skirt …".

Which is rubbish of course. The perpetrator of a crime is the one responsible for carrying it out whatever the circumstances.

But the shouting down of the "victim blamers" can perhaps drown out messages that allow risk reduction, and allow certain myths to be perpetuated. For example, many women believe that they are more at risk from strangers whereas most rapists are known to the victim.

Take a slightly less contentious crime – a phishing spam that criminals use to empty the bank accounts of the victim. Whilst the criminal here is obvious – the person who used stolen credentials to empty the bank account, the criminal needed the victim to make certain risky decisions.

2015-01-29_1517As you cannot look at the link contained within that, it's worth pointing out that if you paste the URL into a notebook, you will get a brazilian site … and I strongly suspect that Lloyds Bank is not very likely to use a Brazilian site (.br) for hosting their online account service.

And we call such victims "gullible". In the case of phishing, there are some simple procedures to follow :-

  1. Email doesn't necessarily come from whom it claims to be from. I can send you an email that will look as if it comes from Goodluck Johnathon without having anything to do with his email account.
  2. Don't click on links in emails.
  3. If your bank sends an email asking you to do something, shut down the email and open a web browser and use your existing way of getting to your bank's web site. Same applies to shopping sites, your workplace's IT department, etc.
  4. If you are determined to use a link from an email, copy the link into a notebook and read it. Does it make sense? Does the first part mention an organisation that has nothing to do with the organisation it is supposedly from? Don't trust it.

Plus a whole bunch more.

Detailing and quantifying risks isn't victim blaming; it's empowering someone to make educated decisions about their behaviour