Game [1.1.3] segfaults on stage separation with this craft

[CorvusCorax]

Hi, I built a craft for use with dark multiplayer, but every time I hit space to engage the 3rd stage, the game segfaults.

The craft was created and edited in the VAB only, using subassemblies that had previously flown on other craft without issues.

To rule out the dmp mod as the culprit, I copied the craft file over to a stock game, stock also segfaults.

I was running KSP_linux.x86_64 on a gentoo linux with Kernel 3.17.7

I then started the x86 version of the game instead of x86_64 and it also segfaults

Game reports as version v1.1.3.1289

Here's the craft file: link to craft file

I tried to backtrace the segfault with gdb, but its not very useful:

	Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff7fbd740 (LWP 5934)]
0x00000000401a62bf in ?? ()
(gdb) bt
#0  0x00000000401a62bf in ?? ()
#1  0x00007ffeff342800 in ?? ()
#2  0x00000000401a61e3 in ?? ()
#3  0x00007fff10fee0b8 in ?? ()
#4  0x00007ffefe052000 in ?? ()
#5  0x00007ffeff342800 in ?? ()
#6  0x00007fff0e297800 in ?? ()
#7  0x0000000016bb5dc0 in ?? ()
#8  0x00000000401a613f in ?? ()
#9  0x0000000000000000 in ?? ()
	

how to reproduce:

1. copy craft file into savegame on stock KSP 1.1.3
2. start the game and load the craft unto the launchpad
3. engage the TR-38-D decoupler between core booster and 3rd stage - either by right-click -> decouple or by going through the staging sequence
4. game segfaults without writing any messages in KSP.log - instead of separating the stages as it should

Edited August 26, 2016 by CorvusCorax
second half was cut off for some reason, re-added

[sal_vager]

Hi @CorvusCorax, this is likely the known issue with the TR-38-D.

Quote

* OSX crash on decoupling the TR-38-D decoupler.

KSP crashes to desktop when decoupling a TR-38-D decoupler.

The TR-38-D decoupler is the only physicsless decoupler in the game, to help reduce wobble on large vessels, but while this decoupler is fine on Windows and Linux it will cause a crash on OSX.

No cause for this crash is known.

Workaround

Edit the part.cfg file in GameData/Squad/Parts/Structural/Size3Decoupler in any text editor.

Change PhysicsSignificance = 1 to PhysicsSignificance = 0

It's rare on Linux, but happens on OSX all the time.

[CorvusCorax]

The workaround indeed makes the segfault disappear.

I also noticed that the game does not crash if I decouple the payload from the upper stage before I activate the TR-38-D (it's a docking port sr, so it can be reattached to the upper stage for circularisation on a trajectory thats lofted enough)

It seems to be one of those rare segfault conditions that are hard to reproduce, changing anything makes it vanish as its delicate conditions are no longer met. I hate those when they happen in my own code

That makes me wonder though if this segfault could be used with a carefully generated craft file to execute arbitrary machinecode on the client - might be mean when sharing crafts on the net or with dark multiplayer and similar mods

would likely be better to get it fixed in the next version before anyone finds out if its exploitable that way

Edited August 26, 2016 by CorvusCorax

[CorvusCorax]

it should be noted that the workaround needs another workaround. Any craft with the TR-28 d becomes almost unflyable with the workaround applied due to wobble. The fix: add struts around the TR-38 D's bottom (connecting to the auto-interstage / engine)

[sal_vager]

Yeah it needs struts, but don't attach struts to the TR-38-D, that summons the Kraken.

The autostruts planned for 1.2 should alleviate this as you won't need a strut on the TR-38-D, or to have them physicsless.