It isn't based on a solid foundation of common interests:
The old saying “politics makes strange bedfellows” is no obvious, alive and mystifying than in Russia and China. It works like this. Russia has long preyed on China and much of far eastern Russia has Chinese claims on it. Yet China is not currently pursuing those claims as it is on its Indian border and in the South China Sea. Russian nukes keeps China from being belligerent and Russian willingness to trade with China and share military technology keeps China friendly. The growing sanctions imposed on Russia because of attempts to rebuild the Russian Empire (in Georgia in 2008 and Ukraine since 2014) has caused an economic crisis in Russia. China is the only major economic power willing to ignore the sanctions and work with Russia. That comes at a price; providing more military tech. China won’t need this tech for long as China will eventually pull ahead of Russia, as it has already done in some areas. But for the moment China is willing to make nice with Russia. At the same time the Russians know that this won’t last and are even now supplying weapons to nations that China is having territorial disputes with.
Well, the Nazi-Soviet pact didn't last very long. And the Nazis won the race for who would break the pact first and attack the other.
So it doesn't seem likely that this friendship can stand the test of time.Unless Russia thinks they are special and they are the one country that China won't pursue territorial claims against.
I'd give this new friendship to 2021, at least.
After that, all bets are off for what becomes an active Chinese "core interest."