Re: [kernel-hardening] [RFC V2 4/6] lib: vsprintf: default kptr_restrict to the maximum value

From: Linus Torvalds
Date: Wed Oct 04 2017 - 15:23:10 EST

On Wed, Oct 4, 2017 at 12:13 PM, Jann Horn <jannh@xxxxxxxxxx> wrote:
> Actually, /proc/kallsyms uses %pK, which hacks around this issue
> by checking for `euid != uid` in addition to the capability check - so this
> isn't exploitable through a typical setuid program.

Fair enough, you'd have to be a pretty broken suid program to have set
uid to euid before reading some untrusted file descriptor.

I could still imagine happening (hey, the X server used to sendmsg
file descriptors back and forth), but hopefully it's not really