Actually, /u/directhex made perfect sense to me as a programmer.

How does:

World read/write /dev/mem in their smartphone camera driver?

Communicate what they're actually trying to talk about without projecting new information onto it? The problem neither relates to /dev/mem nor device files in general. Their followup comment pretty much confirms that when they said that they thought the issue was with the device file's permissions instead of the handling of the device.

That means the device node (I don't know why you keep calling them "device files")

Because that's what the word means.

is sitting on the filesystem of the device, set with world readable/writable permissions.

Incorrect. That's not what the vulnerability is and even if it were then they would've just been wrong about it having to do with drivers. Drivers don't set permissions on device files.

This has nothing to do with a "vulnerability in another part of the kernel." The kernel has nothing to do with the vulnerability.

At no point in all this talking out of your ass did you assume there was someone in the world who doesn't have to do that? That's pretty much explicitly what the person in that forum is talking about. Clearly, even you don't understand what they're talking about.

Are you explaining this based on how you've interpreted the forum post with no programming experience?

Said by the expert programmer that doesn't know that udev sets permissions on device files.

I'm able to understand exactly what the problem is and what /u/directhex was talking about.

Only by assuming they knew what they were talking about.