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Date: Wed, 4 Oct 2017 12:23:02 -0700
From: Linus Torvalds <>
To: Jann Horn <>
Cc: Kees Cook <>, "Tobin C. Harding" <>, 
	Greg KH <>, Petr Mladek <>, 
	Joe Perches <>, Ian Campbell <>, 
	Sergey Senozhatsky <>, 
	"" <>, LKML <>, 
	Catalin Marinas <>, Will Deacon <>, 
	Steven Rostedt <>, William Roberts <>, 
	Chris Fries <>, Dave Weinstein <>
Subject: Re: [RFC V2 4/6] lib: vsprintf: default
 kptr_restrict to the maximum value

On Wed, Oct 4, 2017 at 12:13 PM, Jann Horn <> 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


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