Archive for the ‘Web’ Category

curl, smiley-URLs and libc

Tuesday, February 24th, 2015

Some interesting Unicode URLs have recently been seen used in the wild – like in this billboard ad campaign from Coca Cola, and a friend of mine asked me about curl in reference to these and how it deals with such URLs.

emojicoke-by-stevecoleuk-450

(Picture by stevencoleuk)

I ran some tests and decided to blog my observations since they are a bit curious. The exact URL I tried was ‘www.πŸ˜ƒ.ws’ (not the same smiley as shown on this billboard: πŸ˜‚) – it is really hard to enter by hand so now is the time to appreciate your ability to cut and paste! It appears they registered several domains for a set of different smileys.

These smileys are not really allowed IDN (where IDN means International Domain Names) symbols which make these domains a bit different. They should not (see below for details) be converted to punycode before getting resolved but instead I assume that the pure UTF-8 sequence should or at least will be fed into the name resolver function. Well, either way it should either pass in punycode or the UTF-8 string.

If curl was built to use libidn, it still won’t convert this to punycode and the verbose output says “Failed to convert www.πŸ˜ƒ.ws to ACE; String preparation failed

curl (exact version doesn’t matter) using the stock threaded resolver

  • Debian Linux (glibc 2.19) – FAIL
  • Windows 7 - FAIL
  • Mac OS X 10.9 – SUCCESS

But then also perhaps to no surprise, the exact same results are shown if I try to ping those host names on these systems. It works on the mac, it fails on Linux and Windows. Wget 1.16 also fails on my Debian systems (just as a reference and I didn’t try it on any of the other platforms).

My curl build on Linux that uses c-ares for name resolving instead of glibc succeeds perfectly. host, nslookup and dig all work fine with it on Linux too (as well as nslookup on Windows):

$ host www.πŸ˜ƒ.ws
www.\240\159\152\131.ws has address 64.70.19.202
$ ping www.πŸ˜ƒ.ws
ping: unknown host www.πŸ˜ƒ.ws

While the same command sequence on the mac shows:

$ host www.πŸ˜ƒ.ws
www.\240\159\152\131.ws has address 64.70.19.202
$ ping www.πŸ˜ƒ.ws
PING www.πŸ˜ƒ.ws (64.70.19.202): 56 data bytes
64 bytes from 64.70.19.202: icmp_seq=0 ttl=44 time=191.689 ms
64 bytes from 64.70.19.202: icmp_seq=1 ttl=44 time=191.124 ms

Slightly interesting additional tidbit: if I rebuild curl to use gethostbyname_r() instead of getaddrinfo() it works just like on the mac, so clearly this is glibc having an opinion on how this should work when given this UTF-8 hostname.

Pasting in the URL into Firefox and Chrome works just fine. They both convert the name to punycode and use “www.xn--h28h.ws” which then resolves to the same IPv4 address.

Update: as was pointed out in a comment below, the “64.70.19.202″ IP address is not the correct IP for the site. It is just the registrar’s landing page so it sends back that response to any host or domain name in the .ws domain that doesn’t exist!

What do the IDN specs say?

The U-263A smileyThis is not my area of expertise. I had to consult Patrik FΓ€ltstrΓΆm here to get this straightened out (but please if I got something wrong here the mistake is still all mine). Apparently this smiley is allowed in RFC 3940 (IDNA2003), but that has been replaced by RFC 5890-5892 (IDNA2008) where this is DISALLOWED. If you read the spec, this is 263A.

So, depending on which spec you follow it was a valid IDN character or it isn’t anymore.

What does the libc docs say?

The POSIX docs for getaddrinfo doesn’t contain enough info to tell who’s right but it doesn’t forbid UTF-8 encoded strings. The regular glibc docs for getaddrinfo also doesn’t say anything and interestingly, the Apple Mac OS X version of the docs says just as little.

With this complete lack of guidance, it is hardly any additional surprise that the glibc gethostbyname docs also doesn’t mention what it does in this case but clearly it doesn’t do the same as getaddrinfo in the glibc case at least.

What’s on the actual site?

A redirect to www.emoticoke.com which shows a rather boring page.

emoticoke

Who’s right?

I don’t know. What do you think?

HTTP/2 talk on Packet Pushers

Wednesday, February 18th, 2015

http2 logoI talked with Greg Ferro on Skype on January 15th. Greg runs the highly technical and nerdy network oriented podcast Packet Pushers. We talked about HTTP/2 for well over an hour and we went through a lot stuff about the new version of the most widely used protocol on the Internet.

Listen or download it.

Very suitably published today, the very day the IESG approved HTTP/2.

HTTP/2 is at 5%

Tuesday, February 10th, 2015

http2 logoHere follow some numbers extracted from my recent HTTP/2 presentation.

First: HTTP/2 is not finalized yet and it is not yet in RFC status, even though things are progressing nicely within the IETF. With some luck we reach RFC status within Q1 this year.

On January 13th 2015, Firefox 35 was released with HTTP/2 enabled by default. Firefox was already running it enabled before that in beta and development versions.

Chrome has also been sporting HTTP/2 support in development versions since many moths back where it could easily be manually enabled. Chrome 40 was the first main release shipped with HTTP/2 enabled by default, but it has so far only been enabled for a very small fraction of the user-base.

On January 28th 2015, Google reported to me by email that they saw HTTP/2 being used in 5% of their global traffic (que all relevant disclaimers that this is not statistically safe numbers). This, close after a shaky period with Google having had their HTTP/2 services disabled through parts of the Christmas holidays (due to bugs) – and as explained above, there’s been no time for any mainstream browser to use HTTP/2 by default for very long!

Further data points: Mozilla collects telemetry data from Firefox users who opted-in to it, and it collects numbers on “HTTP Protocol Version Used on Response”. On February 10, it reports that Firefox 35 users have got their responses to report HTTP/2 in 9% of all responses (out of more than 340 billion reported responses). The Telemetry for Firefox Nightly 38 even reports HTTP/2 in 14% of all responses (based on a much smaller sample collection), which I guess could very well be because users on such a bleeding edge version are more experimental by nature.

In these Firefox stats we see that recently, the number of HTTP/2 responses outnumber the HTTP/1.0 responses 9 to 1.

Http2 right now

Sunday, February 1st, 2015

I talked in the Mozilla devroom at FOSDEM 2015. Here are the slides from it. It was recorded on video and I will post a suitable link to that once it becomes available. The talk was meant to be 20 minutes, I think I did it on 22 or something.

http2 explained 1.8

Thursday, January 15th, 2015

I’ve been updating my “http2 explained” document every nohttp2 logow and then since my original release of it back in April 2014. Today I put up version 1.8 which is one of the bigger updates in a while:

http2 explained

The HTTP/2 Last Call within the IETF ended yesterday and the wire format of the protocol has remained fixed for quite some time now so it seemed like a good moment.

I updated some graphs and images to make them look better and be more personal, I added some new short sections in 8.4 and I refreshed the language in several places. Also, now all links mentioned in footnotes and elsewhere should be properly clickable to make following them a more pleasant experience. And page numbers!

As always, do let me know if you find errors, have questions on the content or think I should add something!

Changing networks on Mac with Firefox

Thursday, October 30th, 2014

Not too long ago I blogged about my work to better deal with changing networks while Firefox is running. That job was basically two parts.

A) generic code to handle receiving such a network-changed event and then

B) a platform specific part that was for Windows that detected such a network change and sent the event

Today I’ve landed yet another fix for part B called bug 1079385, which detects network changes for Firefox on Mac OS X.

mac miniI’ve never programmed anything before on the Mac so this was sort of my christening in this environment. I mean, I’ve written countless of POSIX compliant programs including curl and friends that certainly builds and runs on Mac OS just fine, but I never before used the Mac-specific APIs to do things.

I got a mac mini just two weeks ago to work on this. Getting it up, prepared and my first Firefox built from source took all-in-all less than three hours. Learning the details of the mac API world was much more trouble and can’t say that I’m mastering it now either but I did find myself at least figuring out how to detect when IP addresses on the interfaces change and a changed address is a pretty good signal that the network changed somehow.

daniel.haxx.se episode 8

Monday, October 27th, 2014

Today I hesitated to make my new weekly video episode. I looked at the viewers number and how they basically have dwindled the last few weeks. I’m not making this video series interesting enough for a very large crowd of people. I’m re-evaluating if I should do them at all, or if I can do something to spice them up…

… or perhaps just not look at the viewers numbers at all and just do what think is fun?

I decided I’ll go with the latter for now. After all, I enjoy making these and they usually give me some interesting feedback and discussions even if the numbers are really low. What good is a number anyway?

This week’s episode:

Personal

Firefox

Fun

HTTP/2

TALKS

  • I’m offering two talks for FOSDEM

curl

  • release next Wednesday
  • bug fixing period
  • security advisory is pending

wget

Stricter HTTP 1.1 framing good bye

Sunday, October 26th, 2014

I worked on a patch for Firefox bug 237623 to make sure Firefox would use a stricter check for “HTTP 1.1 framing”, checking that Content-Length is correct and that there’s no broken chunked encoding pieces. I was happy to close an over 10 years old bug when the fix landed in June 2014.

The fix landed and has not caused any grief all the way since June through to the actual live release (Nightlies, Aurora, Beta etc). This change finally shipped in Firefox 33 and I had more or less already started to forget about it, and now things went south really fast.

The amount of broken servers ended up too massive for us and we had to backpedal. The largest amount of problems can be split up in these two categories:

  1. Servers that deliver gzipped content and sends a Content-Length: for the uncompressed data. This seems to be commonly done with old mod_deflate and mod_fastcgi versions on Apache, but we also saw people using IIS reporting this symptom.
  2. Servers that deliver chunked-encoding but who skip the final zero-size chunk so that the stream actually never really ends.

We recognize that not everyone can have the servers fixed – even if all these servers should still be fixed! We now make these HTTP 1.1 framing problems get detected but only cause a problem if a certain pref variable is set (network.http.enforce-framing.http1), and since that is disabled by default they will be silently ignored much like before. The Internet is a more broken and more sad place than I want to accept at times.

We haven’t fully worked out how to also make the download manager (ie the thing that downloads things directly to disk, without showing it in the browser) happy, which was the original reason for bug 237623…

Although the code may now no longer alert anything about HTTP 1.1 framing problems, it will now at least mark the connection not due for re-use which will be a big boost compared to before since these broken framing cases really hurt persistent connections use. The partial transfer return codes for broken SPDY and HTTP/2 transfers remain though and I hope to be able to remain stricter with these newer protocols.

This partial reversion will land ASAP and get merged into patch releases of Firefox 33 and later.

Finally, to top this off. Here’s a picture of an old HTTP 1.1 frame so that you know what we’re talking about.

An old http1.1 frame

curl is no POODLE

Friday, October 17th, 2014

Once again the internet flooded over with reports and alerts about a vulnerability using a funny name: POODLE. If you have even the slightest interest in this sort of stuff you’ve already grown tired and bored about everything that’s been written about this so why on earth do I have to pile on and add to the pain?

This is my way of explaining how POODLE affects or doesn’t affect curl, libcurl and the huge amount of existing applications using libcurl.

Is my application using HTTPS with libcurl or curl vulnerable to POODLE?

No. POODLE really is a browser-attack.

Motivation

The POODLE attack is a combination of several separate pieces that when combined allow attackers to exploit it. The individual pieces are not enough stand-alone.

SSLv3 is getting a lot of heat now since POODLE must be able to downgrade a connection to SSLv3 from TLS to work. Downgrade in a fairly crude way – in libcurl, only libcurl built to use NSS as its TLS backend supports this way of downgrading the protocol level.

Then, if an attacker manages to downgrade to SSLv3 (both the client and server must thus allow this) and get to use the sensitive block cipher of that protocol, it must maintain a connection to the server and then retry many similar requests to the server in order to try to work out details of the request – to figure out secrets it shouldn’t be able to. This would typically be made using javascript in a browser and really only HTTPS allows this so no other SSL-using protocol can be exploited like this.

For the typical curl user or a libcurl user, there’s A) no javascript and B) the application already knows the request it is doing and normally doesn’t inject random stuff from 3rd party sources that could be allowed to steal secrets. There’s really no room for any outsider here to steal secrets or cookies or whatever.

How will curl change

There’s no immediate need to do anything as curl and libcurl are not vulnerable to POODLE.

Still, SSLv3 is long overdue and is not really a modern protocol (TLS 1.0, the successor, had its RFC published 1999) so in order to really avoid the risk that it will be possible exploit this protocol one way or another now or later using curl/libcurl, we will disable SSLv3 by default in the next curl release. For all TLS backends.

Why? Just to be extra super cautious and because this attack helped us remember that SSLv3 is old and should be let down to die.

If possible, explicitly requesting SSLv3 should still be possible so that users can still work with their legacy systems in dire need of upgrade but placed in corners of the world that every sensible human has since long forgotten or just ignored.

In-depth explanations of POODLE

I especially like the ones provided by PolarSSL and GnuTLS, possibly due to their clear “distance” from browsers.

Changing networks with Firefox running

Friday, September 26th, 2014

Short recap: I work on network code for Mozilla. Bug 939318 is one of “mine” – yesterday I landed a fix (a patch series with 6 individual patches) for this and I wanted to explain what goodness that should (might?) come from this!

diffstat

diffstat reports this on the complete patch series:

29 files changed, 920 insertions(+), 162 deletions(-)

The change set can be seen in mozilla-central here. But I guess a proper description is easier for most…

The bouncy road to inclusion

This feature set and associated problems with it has been one of the most time consuming things I’ve developed in recent years, I mean in relation to the amount of actual code produced. I’ve had it “landed” in the mozilla-inbound tree five times and yanked out again before it landed correctly (within a few hours), every time of course reverted again because I had bugs remaining in there. The bugs in this have been really tricky with a whole bunch of timing-dependent and race-like problems and me being unfamiliar with a large part of the code base that I’m working on. It has been a highly frustrating journey during periods but I’d like to think that I’ve learned a lot about Firefox internals partly thanks to this resistance.

As I write this, it has not even been 24 hours since it got into m-c so there’s of course still a risk there’s an ugly bug or two left, but then I also hope to fix the pending problems without having to revert and re-apply the whole series…

Many ways to connect to networks

Firefox Nightly screenshotIn many network setups today, you get an environment and a network “experience” that is crafted for that particular place. For example you may connect to your work over a VPN where you get your company DNS and you can access sites and services you can’t even see when you connect from the wifi in your favorite coffee shop. The same thing goes for when you connect to that captive portal over wifi until you realize you used the wrong SSID and you switch over to the access point you were supposed to use.

For every one of these setups, you get different DHCP setups passed down and you get a new DNS server and so on.

These days laptop lids are getting closed (and the machine is put to sleep) at one place to be opened at a completely different location and rarely is the machine rebooted or the browser shut down.

Switching between networks

Switching from one of the networks to the next is of course something your operating system handles gracefully. You can even easily be connected to multiple ones simultaneously like if you have both an Ethernet card and wifi.

Enter browsers. Or in this case let’s be specific and talk about Firefox since this is what I work with and on. Firefox – like other browsers – will cache images, it will cache DNS responses, it maintains connections to sites a while even after use, it connects to some sites even before you “go there” and so on. All in the name of giving the users an as good and as fast experience as possible.

The combination of keeping things cached and alive, together with the fact that switching networks brings new perspectives and new “truths” offers challenges.

Realizing the situation is new

The changes are not at all mind-bending but are basically these three parts:

  1. Make sure that we detect network changes, even if just the set of available interfaces change. Send an event for this.
  2. Make sure the necessary parts of the code listens and understands this “network topology changed” event and acts on it accordingly
  3. Consider coming back from “sleep” to be a network changed event since we just cannot be sure of the network situation anymore.

The initial work has been made for Windows only but it allows us to smoothen out any rough edges before we continue and make more platforms support this.

The network changed event can be disabled by switching off the new “network.notify.changed” preference. If you do end up feeling a need for that, I really hope you file a bug explaining the details so that we can work on fixing it!

Act accordingly

So what is acting properly? What if the network changes in a way so that your active connections suddenly can’t be used anymore due to the new rules and routing and what not? We attack this problem like this: once we get a “network changed” event, we “allow” connections to prove that they are still alive and if not they’re torn down and re-setup when the user tries to reload or whatever. For plain old HTTP(S) this means just seeing if traffic arrives or can be sent off within N seconds, and for websockets, SPDY and HTTP2 connections it involves sending an actual ping frame and checking for a response.

The internal DNS cache was a bit tricky to handle. I initially just flushed all entries but that turned out nasty as I then also killed ongoing name resolves that caused errors to get returned. Now I instead added logic that flushes all the already resolved names and it makes names “in transit” to get resolved again so that they are done on the (potentially) new network that then can return different addresses for the same host name(s).

This should drastically reduce the situation that could happen before when Firefox would basically just freeze and not want to do any requests until you closed and restarted it. (Or waited long enough for other timeouts to trigger.)

The ‘N seconds’ waiting period above is actually 5 seconds by default and there’s a new preference called “network.http.network-changed.timeout” that can be altered at will to allow some experimentation regarding what the perfect interval truly is for you.

Firefox BallInitially on Windows only

My initial work has been limited to getting the changed event code done for the Windows back-end only (since the code that figures out if there’s news on the network setup is highly system specific), and now when this step has been taken the plan is to introduce the same back-end logic to the other platforms. The code that acts on the event is pretty much generic and is mostly in place already so it is now a matter of making sure the event can be generated everywhere.

My plan is to start on Firefox OS and then see if I can assist with the same thing in Firefox on Android. Then finally Linux and Mac.

I started on Windows since Windows is one of the platforms with the largest amount of Firefox users and thus one of the most prioritized ones.

More to do

There’s separate work going on for properly detecting captive portals. You know the annoying things hotels and airports for example tend to have to force you to do some login dance first before you are allowed to use the internet at that location. When such a captive portal is opened up, that should probably qualify as a network change – but it isn’t yet.