Well, Russia is the one who destabilized the Ukraine. They did it to capture an oil pipeline. What Putin didn't expect was for the value of that pipeline to plummet. Originally, having that pipeline would give him leverage against NATO. It also keeps ukraine from joining the EU, which acts as a shield against Russia being invaded. Russia has a historical problem with that. None of this keeps Russia from aiding China. The ukraine situation just isn't that large compared to Russia's military size, plus it is pretty stable.
Russia and China are often enemies anyway. But, china buys a lot of military supplies from Russia. So... Russia might actually benefit from such a war. Their economy isn't doing so well as a result of the Ukraine fuckup, so massive arms sales to China would be great for them.