I'd guess that Russia is able to prevent a surface ship from approaching Russia in any ocean unless someone can fight an offensive air and naval war to get control of that ocean.
I'm guessing (you said "container ship") that the idea might be to use a concealed civilian vessel that then unloads some kind of surprise attack. While disguised military ships have been used to conduct armed warfare before, the last time I can think of an example was British Q-ships in World War I; I'm not sure that this is still legal.
Turkey has closed the Turkish Straits to warships due to the conflict, so technically no warships are supposed to pass, from either side. I'm I believe that it violates the convention governing this to either tell Turkey that the warship isn't actually a warship or if Turkey knows but preferentially lets warships through. That being said, I guess theoretically Ukraine could assemble such an attack using a ship somewhere far away from Ukraine.
My guess is that if Ukraine had a lot of long-range cruise missiles, they'd probably be using them in their own theater of operations, as they're pretty short on them.
I don't think that Russia is using strategic bombers for the glide bombing attacks, so whatever the benefits of hitting them, I'm not sure that it would be a counter to the glide bomb attacks. kagisYeah, this has the (much more numerous) Su-34 being used:
On or just before Thursday, an air force Sukhoi Su-34 fighter-bomber lobbed a single FAB-3000 bomb with pop-out wings and satellite guidance at a multi-story building Russian intelligence had identified as a staging base for Ukrainian troops in Lyptsi, 10 miles north of Kharkiv in northern Ukraine.