1015001 - high CPU usage and disk writes to places.sqlite when DNS for a host is set to 0.0.0.0 in hosts file under Windows

Status: UNCONFIRMED

(Core :: Networking: DNS, defect, P5)

Description

[abandoned account]

Attachment: hosts

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0 (Beta/Release)
Build ID: 20140520115057

Steps to reproduce:

1. make sure firefox is not running (to be sure)
2. edit hosts file(C:\Windows\System32\drivers\etc\hosts.) and make sure only the following two lines exist (or maybe just one is enough):
127.0.0.1       localhost
0.0.0.0	instagram.com

3. the DNS Service (in windows 7 64bit that is) was disabled, for me - not sure if this matters much
4. regardless of what dns server(s) are set for your connection(LAN, for me) (tested 8.8.8.8 and then 127.0.0.1 unbound+dnscrypt; not at the same time)
start firefox
5. new tab (Ctrl+T) and type in the address bar(Alt+D):
instagram.com
press enter and observe

I'm on Windows 7 64bit... firefox 30, beta6? (on beta channel, latest at the time)



Actual results:

firefox starts using 25% cpu (on a quad core) and the tab "title" is "Connecting..."  
this happens indefinitely (apparently)
and unless places.history.enabled  (in about:config) is set to false, then there is huge amount of writes on disk(SSD in my case) to the file(s):
places.sqlite
places.sqlite-wal
(maybe others? can't remember, but I was using Resource Monitor from windows and it says 33,000,000 more or less, B/sec at the Writes section)

I also notice there's a status saying:
Waiting for instagram.com ...

maybe worth noting that nslookup instagram.com returns correct ip, but I guess, it makes sense because firefox actually uses hosts file first, and that's why it sees 0.0.0.0 instead, that's great.


I've notice that if I put another hostname like mooshworld.com  the cpu usage and disk writes were less, like 11% cpu and 1.2mb for disk writes. Which is kinda odd? maybe it depends on my history in places? no idea



Expected results:

perhaps it should act as it does when the value 0.0.0.0 is 127.0.0.1 
and in this case it just shows the Unable to connect page:
Firefox can't establish a connection to the server at instagram.com.

or at the very least, not write that crazily :)) on the disk and also not use that much cpu

apparently changing from 0.0.0.0 to 127.0.0.1 while firefox is running worked - that is, without restarting firefox.

Also note, when the `Unable to connect` page is displayed, pressing `Try again` button won't have the same effect as typing in `instagram.com` in a new tab, that is when changing back from 127.0.0.1 to 0.0.0.0 , it will still act as if 127.0.0.1 is happening and just keep showing the Unable to connect page and not trigger the bug. Well actually it shows the `Server not found` page when it is set to 0.0.0.0 and you press the `Try again` button, but it's still instantly and no bug. 

New tab(Ctrl+T) and Alt+D(focus address) and type "instagram.com"  triggers the bug again, without firefox restart - nice that it can see the change in hosts.

Comment 1

[abandoned account]

oh wait, I will disable all addons (I had no plugins, neither enabled nor disabled, list is empty)
and see if it still happens - why didn't I think of this before?

Comment 2

[abandoned account]

confirmed, it still happens without any addons(and any plugins)
the cpu usage is 28-34 % (on quad core) and I still had places.history.enabled=false  the B/s write was maybe 60KB/sec for sessionstore.js or something like that
the status was: Looked up instagram.com...  (and was still loading: icon was animating)

Comment 3

[abandoned account]

made another test case to be sure it's not related to the `hosts` file explicitly, but rather in general whenever a site resolves to 0.0.0.0  

I can confirm that by having Unbound(local dns server) reply with 0.0.0.0 for instagram.com  the same thing happens as if it were in the `hosts` file.

in this case nslookup also returned 0.0.0.0
C:\Users\user>nslookup instagram.com
Server:  localhost
Address:  127.0.0.1

Name:    instagram.com
Address:  0.0.0.0


I'll include the used .conf file for unbound, just in case someone(or future me or wtw) wants to try that variant.

Comment 4

[abandoned account]

Attachment: Unbound(dns server) config file to emulate the same thing in `hosts` file, ie.: 0.0.0.0 instagram.com

Comment 5

[Firefox Bug Husbandry Bot]

Bulk change to priority: https://bugzilla.mozilla.org/show_bug.cgi?id=1399258

Comment 6

[Danial Horton]

This can be closed, it was either fixed long ago or something else had gone wrong on the original submitters computer.