when the new kernel comes out Linux users will be safe
It’s going to take a lot longer than that for most distros to move to latest upstream. This specific fix might be pulled in as a hotfix if you’re lucky, but it still takes time. The latest Ubuntu LTS is on 5.15, for example, which was released in October 2021. Debian Bookworm, which just released last month, uses 6.1 from December 2022.
This is exactly the kind of thing that gets backported to stable LTS distros tho. The kernel Major.Minor is just the base - it doesn’t tell the whole story.
Critical security fixes are backported. There where a lot of kernels released yesterday that had the fix. For 5.15, 5.15.122 was released with the zenbleed mitigation.
5.15.122 was released with the zen bleed mitigation
But Ubuntu users (for example) won’t get that automatically. Canonical still has to pull the upstream release, run validation, and roll out a patch. It will probably be speedy, but still on the order of several weeks before people see it by default.