[Problem]: segmentation fault when a frame sync error is too large

[mdickers47]

What happened?

Mainly, shairport-sync is working great. Thank you! I had a problem where it was seg faulting repeatedly. I can't reproduce it now, but it might be obvious given this description:

The last message was "warning: Failed to allocate memory for a final_adjustment_silence buffer of xxxx frames", where xxxx was a ridiculously large 9 or 10 digit number.

I found this was being caused by a desktop using libpipewire-module-raop-discover, which had been set to use the shairport-sync airplay target. Every time shairport-sync restarts, libpipewire-module-raop-discover immediately reconnects. I speculate that it then tries to resume the previously crashed stream, with invalid timestamps that caused shairport-sync to calculate a bogus correction offset, thus it tried to malloc a jillion bytes and seg faulted.

The relevant code looks like player.c 2786 to 2809. This is probably dumb behavior from pipewire, but maybe you see a way to handle it that is more graceful than seg fault.

Relevant log output

System Information.

Raspberry Pi 4b 2GB, Alpine Linux 3.22, hifiberry DAC

Configuration Information.

>> Display Config Start.

From "uname -a":
 Linux pi4b.domain.com 6.12.38-0-rpi #1-Alpine SMP PREEMPT Tue Jul 15 10:07:54 UTC 2025 aarch64 Linux

From /etc/os-release:
 Alpine Linux v3.22

From /sys/firmware/devicetree/base/model:
 Raspberry Pi 4 Model B Rev 1.1

Shairport Sync Version String:
 4.3.7-OpenSSL-Avahi-ALSA-pa-pw-stdout-pipe-soxr-metadata-dbus-mpris-sysconfdir:/etc

Command Line:
 shairport-sync --displayConfig

Configuration File:
 /etc/shairport-sync.conf

Configuration File Settings:
 general : 
 {
   name = "Audiplex";
   default_airplay_volume = -6.0;
 };
 alsa : 
 {
   output_device = "hw:0";
 };
 pw : 
 {
 };

>> Display Config End.
>> Goodbye!

PulseAudio or PipeWire installed?

• Check if your system uses a Sound Server.

How did you install Shairport Sync?

A package manager (apt, apt install, yum, pkg, etc.)

Check previous issues

• Confirm

[mikebrady]

Thanks for the report -- I'll take a look. If you got a chance to capture the number xxxx at some stage, it would be useful -- maybe it's a sign overflow problem, and the magnitude might be a hint.

[mikebrady]

So, I've been taking an initial look at this.

1. There are two formatting errors in the warning message code that starts at player.c:2805 -- apologies. It should read:

                 warn("Failed to allocate memory for a final_adjustment_silence buffer of %u "
                      "frames for a "
                      "sync error of %" PRId64 " frames.",
                      final_adjustment_length_sized, sync_error);
   

2. The problem doesn't seem to occur in the development version of Shairport Sync.
3. However, there is a problem with the PipeWire module that is exposed by the development version of Shairport Sync. The problem is that the ALAC encoder in the PipeWire module appears to be faulty -- it omits the terminal token of an ALAC packet. The decoders used in Shairport Sync up until now ignored this fault, but the FFmpeg decoder which is now recommended for use with the development version of classic Shairport Sync (and which is mandatory for the AirPlay 2 version) rejects these packets. So you would have to (1) build the development version for classic AirPlay only and (2) build it without the recommended --with-ffmpeg flag. (I guess that the PipeWire module is still using a non-FFmpeg ALAC encoder.)

[mikebrady]

Just filed an issue with the PipeWire developers -- please see https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/4853.

[mdickers47]

Cool, that all makes sense. I will get the large number if the crash happens again, although it sounds like the warning message was garbled and the problem is solved anyway. Thanks!

[mikebrady]

Just filed an issue with the PipeWire developers -- please see https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/4853.

FYI this issue that been dealt with by the PipeWire guys, which is great!