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SubjectRe: High UID support for Linux
Albert D. Cahalan wrote:
> Besides trunctuation (aliasing), we get sign extension.
> After some 16-bit abuse, 0x0001ffff can become 0xffffffff
> (UID -1 is special) and 0x12340000 can become 0.

That's why the safest thing is to just go 32-bit in the kernel completely
and DON'T try to second guess what userland really meant.

> What about when an old server with 16-bit UIDs checks for root?
> This isn't just a kernel problem. I could imagine sudo giving out
> access to users 0x00001234, 0x10001234, and 0x0a001234.

If a high UID process calls sys_oldgetuid(), SIGKILL it. Harsh, but safe.

-Mitch

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