Tag Archives: Apple

poll on mac 10.12 is broken

When Mac OS X first launched they did so without an existing poll function. They later added poll() in Mac OS X 10.3, but we quickly discovered that it was broken (it returned a non-zero value when asked to wait for nothing) so in the curl project we added a check in configure for that and subsequently avoided using poll() in all OS X versions to and including Mac OS 10.8 (Darwin 12). The code would instead switch to the alternative solution based on select() for these platforms.

With the release of Mac OS X 10.9 "Mavericks" in October 2013, Apple had fixed their poll() implementation and we've built libcurl to use it since with no issues at all. The configure script picks the correct underlying function to use.

Enter macOS 10.12 (yeah, its not called OS X anymore) "Sierra", released in September 2016. Quickly we discovered that poll() once against did not act like it should and we are back to disabling the use of it in preference to the backup solution using select().

The new error looks similar to the old problem: when there's nothing to wait for and we ask poll() to wait N milliseconds, the 10.12 version of poll() returns immediately without waiting. Causing busy-loops. The problem has been reported to Apple and its Radar number is 28372390. (There has been no news from them on how they plan to act on this.)

poll() is defined by POSIX and The Single Unix Specification it specifically says:

If none of the defined events have occurred on any selected file descriptor, poll() waits at least timeout milliseconds for an event to occur on any of the selected file descriptors.

We pushed a configure check for this in curl, to be part of the upcoming 7.51.0 release. I'll also show you a small snippet you can use stand-alone below.

Apple is hardly alone in the broken-poll department. Remember how Windows' WSApoll is broken?

Here's a little code snippet that can detect the 10.12 breakage:

#include <poll.h>
#include <stdio.h>
#include <sys/time.h>

int main(void)
{
  struct timeval before, after;
  int rc;
  size_t us;

  gettimeofday(&before, NULL);
  rc = poll(NULL, 0, 500);
  gettimeofday(&after, NULL);

  us = (after.tv_sec - before.tv_sec) * 1000000 +
    (after.tv_usec - before.tv_usec);

  if(us < 400000) {
    puts("poll() is broken");
    return 1;
  }
  else {
    puts("poll() works");
  }
  return 0;
}

Follow-up, January 2017

This poll bug has been confirmed fixed in the macOS 10.12.2 update (released on December 13, 2016), but I've found no official mention or statement about this fact.

curl and h2 on mac

$ curl ‐‐http2 https://daniel.haxx.se/
curl: (1) Unsupported protocol

curl on mac

curcurl-symboll has been shipped by default on Mac OS X since many years - I actually couldn't even manage to figure out exactly how many. It is built and bundled with the operating system by Apple itself and on Apple's own terms and even though I'm the main curl developer I've never discussed this with them or even been asked or told about their plans. I'm not complaining, our license allows this and I'm nothing but happy with them shipping curl to millions of Mac users.

Leaving OpenSSL

osxOriginally, curl on Mac was built against OpenSSL for the TLS and SSL support, but over time our friends at Apple have switched more and more of their software over to use their own TLS and crypto library Secure Transport instead of OpenSSL. A while ago Apple started bundling curl built to use the native mac TLS library instead of OpenSSL.

As you may know, when you build curl you can select from eleven different TLS libraries and one of them of course is Secure Transport. Support for this TLS back-end in curl was written by curl hackers, but it apparently got to a quality level good enough for Apple to decide to build curl with this back-end and ship it like that.

The Secure Transport back-end is rather capable and generally doesn't cause many reasons for concern. There's however one notable little glitch that people keep asking me about...

curl doesn't support HTTP/2 on mac!

There are two obvious reasons why not, and they are:

1. No ALPN with Secure Transport

Secure Transport doesn't offer any public API to enable HTTP/2 with ALPN when speaking HTTPS. Sure, we know Apple supports HTTP/2 already in several other aspects in their ecosystem and we can check their open code so we know there's support for HTTP/2 and ALPN. There's just no official APIs for us to use to switch it on!

So, if you insist on building curl to use Secure Transport instead of one of the many alternatives that actually support ALPN just fine, then you can't negotiate HTTP/2 over TLS!

2. No nghttp2 with Mac OS

Even without ALPN support, you could actually still negotiate HTTP/2 over plain text TCP connections if you have a server that supports it. But even then curl depends on the awesome nghttp2 library to provide the frame level protocol encoding/decoding and more. If Apple would decide to enable HTTP/2 support for curl on Mac OS, they need to build it against nghttp2. I really think they should.

Homebrew and friends to the rescue!

Correct. You can still install your own separate curl binary (and libcurl library) from other sources, like for example Homebrew or Macports and they do offer versions built against other TLS back-ends and nghttp2 and then of course HTTP/2 works just fine with curl on mac.

Did I file a bug with Apple?

No, but I know for certain that there has been a bug report filed by someone else. Unfortunately it isn't public so I can't link nor browse it.

Changing networks on Mac with Firefox

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.

Apple’s modified CA cert handling and curl

I tweeted about me finding a change in Apple's version of curl that I haven't seen any public patch for. Apple otherwise hosts a whole slew of curl patches which they never discuss with us about but still make public and we can see what they did.

I was trying to help out a fellow curl user on IRC (we're in #curl on freenode, come see us) and he was trying to understand some funny effects of running curl against a HTTPS site and he showed me the output from a "curl -v" log. The verbose log curiously was different than mine (same curl version built by myself on Linux). My conclusion was that something was different in the Apple version.

The users log said:

* About to connect() to host.example.com port 443 (#0)
*   Trying 1.2.3.4... connected
* Connected to host.example.com (1.2.3.4) port 443 (#0)
* SSLv3, TLS handshake, Client hello (1):

... while my command against the same site said:

* About to connect() to host.example.com port 443 (#0)
*   Trying 1.2.3.4... connected
* Connected to host.example.com (1.2.3.4) port 443 (#0)
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: none
* SSLv3, TLS handshake, Client hello (1):

(I've bolded the part my output showed that wasn't in the mac version, the real host name and IP have been changed.)

It seems I was wrong however.

The output above is only shown if libcurl sets the CA cert path to OpenSSL and it seems the Mac version doesn't. Somehow they get the CA certs loaded to libcurl differently.

So ok, maybe they didn't modify curl but they certainly changed how curl uses CA certs and they did this by modifying OpenSSL and clearly their version of OpenSSL now defaults to use their CA cert bundle. The end result for me is still the same though: I have no idea how CA certs work with curl on Mac so it leaves me with the unfortunate situation where I can't help fellow curl users when they have CA cert problems on a Mac.

It also leaves me very curious on what --cacert does exactly on the mac version of curl.

OpenSSL is patched. Apparently it now works so that if the "normal" x509 validation fails, and TrustEvaluationAgent (TEA) is enabled, it will attempt to use the TEA to validate the certificate. The apple source code to read through for this is x509_vfy_apple.c in their patched OpenSSL tree. It is also possible to skip the TEA verification thing in OpenSSL by setting an environment variable, so that we can still have curl on mac act "as default" with a command line like:

$ env OPENSSL_X509_TEA_DISABLE=1 curl https://www.example.com/

Finally: yes, curl is released under an MIT license. They're perfectly allowed to do whichever of these actions they want. I know this, and I chose the MIT license fully aware that any company can take the code, modify it and never return any changes. I'm not arguing against anyone's rights to do this with curl.

Thank you, friendly anonymous helper for helping me straighten out my findings!

Apple – only 391 days behind

In the curl project, we take security seriously. We work hard to make sure we don't open up for security problems of any kind and once we fail, we work hard at analyzing the problem and coming up with a proper fix as swiftly as possible to make our "customer" as little vulnerable as possible.

Recently I've been surprised and slightly shocked by the fact that a lot of open source operating systems didn't release any security upgrades to our most recent security flaw until well over a month after we first publicized the flaw. I'm not sure why they all reacted so slowly. Possibly it is because vendor-sec isn't quite working as they were informed prior to the notification, and of course I don't really expect many security guys to be subscribed to the curl mailing lists. Slow distros include Debian and Mandriva while Redhat did great.

Today however, I got a mail from Apple (and no, I don't know why they send these mails to me but I guess they think I need them or something) with the subject "APPLE-SA-2010-03-29-1 Security Update 2010-002 / Mac OS X v10.6.3". Aha! Did Apple now also finally update their curl version you might think?

They did. But they did not fix this problem. They fixed two previous problems universally known as CVE-2009-0037 and CVE-2009-2417. Look at the date of that first one. March 3, 2009. Yes, a whopping 391 days after the problem was first made public, Apple sends out the security update. Cool. At least they eventually fixed the problem...