Category Archives: Linux

Everything related to Linux really

cURL and libcurl, Linux

Fedora and curl-minimal

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(This blog post has been updated a few times after the initial publication.)

In the Fedora project there is/was a proposal to introduce a curl-minimal package (and its companion libcurl-minimal) by default, as a way to provide default packages with smaller security risk areas. The full curl version packages would then be offered next to the minimal ones and require users to opt-in. (Related article on lwn.net)

The proposal is for making curl-minimal the default for “non-containerized installations of Fedora”. The curl-minimal packages already exists since 2017. Kamil Dudka had a talk about it at curl-up 2018.

curl-minimal would disable lesser used protocols and features. The discussion around exactly which parts it should disable is ongoing. The proposal to make it default was at least initially shut down by the Fedora Steering Committee on March 8, 2022 but I get the sense the curl-minimal idea have not died yet.

Balance

The balance is really tricky but yet seems to be the key to if this is going to be a worthwhile effort or not.

Disabling too many things in the name of security will make many more users install the full package, and then there is no security gain.

Enabling too many things in the minimal version makes it less of a security gain to begin with.

Security

The harsh truth about past security problems in curl and libcurl, is that most of them were found in components and parts that this minimal package would include.

The question is really how much a minimal package will actually save users from risk and not just cause endless amounts of friction going forward.

Not to mention that since Fedora aims to provide the full package as well, they will not avoid the risk of security problems even in the parts that are disabled in the minimal version. They can only reduce the impact of such flaws.

Features

It is really hard for packagers to know what curl features that are used and not used. There simply is no way to find out, besides shipping a version and listening to the screams of users in pain when things break. It will also force them into line-drawing decisions such as “only N users seem to use feature Z so let’s keep that in the full package” and figuring out the N number is a fuzzy estimate at best.

Some curl features are generally assumed to be there by tools and environments. An example is how a lot of tools and services, like for example web browsers, these days offer copy-as-curl functions. They put a generated curl command line in the clipboard so that users can paste that command in a shell prompt to reproduce an operation with curl.

If those generated command lines stop working because the newly installed curl package doesn’t have feature Z enabled while the generated curl command lines uses it, that’s going to make users unhappy.

The worst part for us in the curl project is probably that this is ultimately going to lead to an increased number of bug reports to the curl project because people will not understand why or how things go wrong.

Nobody asked us

Neither the curl project nor me personally have been asked or prompted for our views or feedback on this. It seems the Fedora people have not even considered the little and uncertain numbers on curl usage that exist – namely the results from the annual curl user surveys.

The 2021 analysis is here.

Update: I have been informed they are using that data and results as input. I was wrong above.

Loadable modules is not the fix

In the lwn comments on this topic, several people brought up that the curl project could “fix this” by making the support for different protocols into separate loadable modules, as then people could chose to only install the modules for the particular protocols they want.

That wouldn’t solve the issue at all. That would then instead just push users into installing several different protocol modules instead of minimal vs full. It would still be the same “this application suddenly broke because its needs YYY from libcurl”. Plus, the discussion around the curl-minimal package goes into more details and features than just protocols, and we can’t do every single feature a loadable module.

I have no intention of working on loadable modules for libcurl – for anything. That’s just a lot of work for no obvious benefit and it will introduce lots of new error and problem surfaces to users and it will not be possible to support on all platforms so it also needs to be provided conditionally.

Will curl-minimal happen?

I don’t know.

Linux, Open Source

Rpi night in GBG

pelagicore logo

Daniel talking So I flew down to and participated at yet another embedded Linux hacking event that was also co-organized by me, that took place yesterday (November 20th 2013) in Gothenburg Sweden.

The event was hosted by Pelagicore in their nice downtown facilities and it was fully signed up with some 28 attendees.

I held a talk about the current situation of real-time and low latency in the Linux kernel, a variation of a talk I’ve done before and even if I have modified it since before you can still get the gist of it on this old slideshare upload. As you can see on the photo I can do hand-wavy gestures while talking! When I finally shut up, we were fed tasty sandwiches and there was some time to socialize and actually hack on some stuff.

Embedded Linux hackers in GBG

I then continued my tradition and held a contest. This time I did raise the complexity level a bit as I decided I wanted a game with more challenges and something that feels less like a quiz and more like a game or a maze. See my separate post for full details and for your chance to test your skills.

This event was also nicely synced in time with the recent introduction of the foss-gbg mailing list, which is an effort to gather people in the area that have an interest in Free and Open Source Software. Much in the same way foss-sthlm was made a couple of years ago.

Pelagicore also handed out 9 Raspberry Pis at the event to lucky attendees.

Linux, Open Source

Embedded and Raspberry Pis in GBG

Kjell Ericson's blinking leds

On November 20, we’ll gather a bunch of interested people in the same room and talk embedded Linux, open source and related matters. I’ll do a talk about real-time in Linux and I’ll run a contest in the same spirit as I’ve done before several times.

Sign-up here!

Pelagicore is hosting and sponsoring everything. I’ll mostly just show up and do what I always do: talk a lot.

So if you live in the area and are into open source and possibly embedded, do show up and I can promise you a good time.

(The photo is actually taken during one of our previous embedded hacking events.)

Development, Haxx, Linux, Open Source

Another embedded hacking day

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enea We started off this second embedded hacking day (the first one being the one we had in October) when I sent out the invitation email on April 22nd asking people to sign up. We limited the number of participants to 40, and within two hours all seats had been taken! Later on I handed out more tickets so we ended up with 49 people on the list and interestingly enough only 13 of these were signed up for the previous event as well so there were quite a lot of newcomers.Daniel Stenberg, a penguin

Arrival

At 10 in the morning on Saturday June 1st, the first people had already arrived and more visitors were dropping in one by one. They would get a goodie-bag from our gracious host with t-shirt (it is the black one you can see me wearing on the penguin picture on the left), some information and a giveaway thing. This time we unfortunately did not have a single female among the attendees, but the all-male crowd would spread out in the room and find seating, power and switches to use. People brought their laptops and we soon could see a very wide range of different devices, development boards and early design ideas showing up on the tables. Blinking leds and cables everywhere. Exactly the way we like it!

A table full of hackers and equipment!

Giveaway

A USB wifi thing

We decided pretty early on the planning for this event that we wouldn’t give away a Raspberry Pi again like we did last time. Not that it was a bad thing to give away, it was actually just a perfect gift, but simply because we had already done that and wanted to do something else and we reasoned that by now a lot of this audience already have a Raspberry pi or similar device.

So, we then came up with a little device that could improve your Raspberry Pi or similar board: a USB wifi thing with Linux drivers so that you easily can add wifi capabilities to your toy projects!

And in order to provide something that you can actually hack on during the event, we decided to give away an Arduino Nano version. Unfortunately, the delivery gods were not with us or perhaps we had forgot to sacrifice the correct animal or something, so this second piece didn’t arrive in time. Instead we gathered people’s postal addresseAns and once the package arrives in a couple of days we will send it out to all attendees. Sort of a little bonus present afterwards. Not the ideal situation, but hey, we did our best and I think this is at least a decent work-around.

So the fun begun

In the big conference room next to the large common room, I said welcome to everyone at 11:00 before I handed over to Magnus from Xilinx to talk about Xilinx Zynq and combining ARM and FPGAs. Magnus Lindblad, Xilinx The crowd proved itself from the first minute and Magnus got a flood of questions immediately. Possibly it was also due to the lovely combo that Magnus is primarily a HW-guy while the audience perhaps was mostly SW-persons but with an interest in lowlevel stuff and HW and how to optimize embedded systems etc.

Audience listening to Magnus

After this initial talk, lunch was served.

Contest

I got lots of positive feedback the last time on the contest I made then, so I made one this time around as well and it was fun again. See my separate post on the contest details.

Flying

After the dust had settled and everyones’ pulses had started to go back to normal again after the contest, Björn Stenberg “took the stage” at 14:00 and educated us all in how you can use 7 Arduinos when flying an R/C plane.

Björn talks about open source flying

Björn Stenberg, a penguin

It seemed as if Björn’s talk really hit home among many people in the audience and there was much talking and extra interest in Björn’s large pile of electronics and “stuff” that he had brought with him to show off. The final video Björn showed during his talk can be found here.

Stuff to eat

Buns for the masses!People actually want to get something done too during a day like this so we can’t make it all filled up with talks. Enea provided candy, drinks and buns. And of course coffee and water during the entire day.

Even with buns and several coffee refills, I think people were slowly getting soft in their brains when the afternoon struck and to really make people wake up, we hit them with Erik Alapää’s excellent talk…

Aliasing in C and C++

Or as Erik specified the full title: “Aliasing in C99/C++11 and data transfer between hard real-time systems on modern RISC processors”…

Erik helped put the light on some sides of the C programming language that perhaps aren’t the most used or understood. How aliasing can be used and what pitfalls it can send us down into!

Erik Alapää on C aliasing

Kjell Ericson's blinking ledsPersonally I don’t really had a lot of time or comfort to get much done this day other than making sure everything ran smooth and that everyone was happy and the schedule was kept. My original hopes was to get some time to do some debugging on a few of my projects during the day but I failed that ambition…

We made sure to videofilm all the talks so we should hopefully be able to provide online versions of them later on.

Real-time Linux

I took the last speaker slot for the day. I think lots of brains were soft by then, and a few people had already started to drop off. I talked for a while generically about how the real-time problem (or perhaps low-latency) is being handled with Linux these days and explained a bit about PREEMPT_RT and full dynamic ticks and what the differences of the methods are.

Daniel Stenberg talks Real-time Linux

The end

At 20:00 we forced everyone out of the facilities. A small team of us grabbed a bite and a couple of beers to digest the day and to yap just a little bit more before we split up for the evening and took off home…

Thank you everyone who was there for making it another great event. Thank you all speakers for giving the event the extra brightness! Thank you Enea for sponsoring, hosting and providing all the goodies in such an elegant manner! It is indeed possible that we make a 3rd embedded hacking day in the future…

Development, Linux, Open Source

Embedded hacking contest #2, decoded

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Okay, so here are the correct answers to the embedded hacking #2 contest (click for larger pictures):

The contests correct answers marked

The fact that you get the clues as hexadecimal uppercase ASCII was pretty quickly clear to everybody. I found it interesting to hear how people attacked the problem of decoding the hex into letters. Most people seem to have made a lookup-table fairly soon, and at least one contestant I talked to made a mistake in his table that turned W into X instead! This year’s winner did the conversion completely without a written down table…

So all the pieces are decoded like this:

The final question

Of course, now a pedant would argue that FORK() isn’t correct, but I decided to use all uppercase just to make the conversion slightly easier. At least I think converting only uppercase ASCII as hex is easier. So the question is “What does fork() return in the child process?”

The answer to the question is 0 (zero). Short and simple. See fork’s man page.

Linus Nielsen Feltzing is the happy winner!

After 13 minutes and 20 seconds since I clicked start on the timer, Linus Nielsen Feltzing approached me with a little note with the correct answer and we had a winner!

The very happy Linus was very disappointed in the previous competition when he was very close to winning but was beaten just within seconds by last time’s winner.

Now, the Chromebook that Enea donated to the winner of the contest was handed over to Linus. (The Samsung Cortex-A15 version.)

Development, Linux, Open Source

Embedded hacking contest #2

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eneaI created another contest for the Embedded hacking event we just pulled off again, organized with foss-sthlm and Enea. Remember that I made one previously at our former hacking day?

The lesson from that time was that the puzzle ingredient then was slightly too difficult so people had to work a bit too long. It made many people give up and the ones who didn’t had to spend a significant time on solving it.

This time, I decided to use the same basic principle: ask N questions that all provide hints for the (N+1)th question, so that the first one to give me the answer to that final question is the winner. It makes it very easy for me to judge and it is a rather neat competition style game. I decided 10 questions should be enough.

To reduce some of the complexity from last time, I decided to provide the individual clues in the correct chronological order but instead add another twist: they aren’t in plain text! But since they’re chronological, the participants can go back and quite “easily” try other alternatives if there are some strange words appearing in the output. I made sure that all alternatives always have fine English alternatives so that if you pick the wrong answer it might still sound or look like English for a while…

I was very happy to see over 30 persons in the room that decided to accept the challenge. I suspect the prize did its part in attracting people to give it a go.

The rules in slightly longer terms as I put them (click it to see a higher resolution version):

the rules

And I clarified how the questions work:

the-questions

I then started my timer, and I showed all the questions on the projector to everyone. I gave them around 40 seconds per question. It thus took almost seven minutes to go through them and then I left a final slide up showing all questions:

The 10 questions

To allow readers to give this contest a go first before checking the answers. See the full answer and explanation.

A room full of competitive hackers

Linux, Open Source, Rockbox

Videos from the embedded hacking day

Here are the videos from the embedded Linux hacking day foss-sthlm arranged on October 20th 2012. They are all speaking Swedish:

Linux och open source inom inbyggda system

med Daniel Stenberg

Yocto-projektet

med Björn Stenberg

Utveckling och trender av multicorekretsar inom halvledarindustrin

med Jonas Svennebring

Reverse engineering Рegen kod p̴ andras h̴rdvara

med Linus Nielsen Feltzing

Development, Linux, Open Source

Embedded Linux Contest

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During our embedded Linux hacking event in Stockholm on October 20th I ran a little contest for the ones who wanted to participate. I created it entirely by myself to allow as many people as possibly to participate with them knowing me or me knowing them etc limiting the fun.

For your amusement I include the full contest here. If you want to try it out, then make sure you don’t attempt to google for any answers or otherwise use a machine/computer as a help.

img1

img2

img3

Here I just want to mention that, as is shown in the above example question, ‘ace‘ is the correct character sequence and the letters should then be kept in that order in the final question. Also note that a character sequence can legally contain a dash as well. You will get 16 similar sequences of 1 to 3 letters, and those 16 sequences should be moved around to form the 17th question.

img4

… at this point I fired off all the questions one by one at about 15-20 seconds per question. In this blog post I’ll take a shortcut and instead show you the final page I made that showed all questions at once, which I then left displayed for the remainder of the competition time. Click the image to get a full resolution version that is perfectly readable:

all questions at once

the winners of the contest

My take away from this contest is that it was harder than I anticipated and took a longer time to crack than I thought. I gave away a few additional clues and hints as the time went by, but in the end I believe there were several persons who were very close to breaking it at almost the same time. In the end, Klas and Jonas presented the correct answer first and won the bottle of Champagne. I’m sure you appreciate their efforts after having tried this yourself!

The answers? Are you really sure? The correct answers and the final question with its answer is available…

I had a great time creating the competition and I believe the competitors appreciated it.

Additional trivia: I created the letter sequences for the other alternatives by writing other English phrases and chopped them up, so that they were from actual English and hence possibly more believable.

Linux

Linux kernel code on TV

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In one of the fast-moving early scenes in episode 16 of Person of Interest at roughly 2:05 into the thing I caught this snapshot:

person of interest s01e16

(click the image to see a slightly bigger version)

It is only in sight for a fraction of a second. What is seen in the very narrow terminal screen on the right is source code scrolling by. Which source code you say? Take a look again. That my friends is kernel/groups.c from around line 30 in a recent Linux kernel. I bet that source file never had so many viewers before, although perhaps not that many actually appreciated this insight! 😉

And before anyone asks: no, there’s absolutely no point or relevance in showing this source code in this section. It is just a way for the guys to look techy. And to be fair, in my mind kernel code is fairly techy!

Haxx, Linux

Travel for fun or profit

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As a protocol geek I love working in my open source projects curl, libssh2, c-ares and spindly. I also participate in a few related IETF working groups around these protocols, and perhaps primarily I enjoy the HTTPbis crowd.

Meanwhile, I’m a consultant during the day and most of my projects and assignments involve embedded systems and primarily embedded Linux. The protocol part of my life tends to be left to get practiced during my “copious” amount of spare time – you know that time after your work, after you’ve spent time with your family and played with your kids and done the things you need to do at home to keep the household in a decent shape. That time when the rest of the family has gone to bed and you should too but if you did when would you ever get time to do that fun things you really want to do?

IETF has these great gatherings every now and then and they’re awesome places to just drown in protocol mumbo jumbo for several days. They’re being hosted by various cities all over the world so often I deem them too far away or too awkward to go to, also a lot because I rarely have any direct monetary gain or compensation for going but rather I’d have to do it as a vacation and pay for it myself.

IETF 83 is going to be held in Paris during March 25-30 and it is close enough for me to want to go and HTTPbis and a few other interesting work groups are having scheduled meetings. I really considered going, at least to meet up with HTTP friends.

Something very rare instead happened that prevents me from going there! My customer (for whom I work full-time since about six months and shall remain nameless for now) asked me to join their team and go visit the large embedded conference ESC in San Jose, California in the exact same week! It really wasn’ t a hard choice for me, since this is my job and being asked to do something because I’m wanted is a nice feeling and position – and they’re paying me to go there. It will also be my first time in California even though I guess I won’t get time to actually see much of it.

I hope to write a follow-up post later on about what I’m currently working with, once it has gone public.