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Date: Wed, 4 Oct 2017 21:13:39 +0200
From: Jann Horn <>
To: Linus Torvalds <>
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 7:28 PM, Linus Torvalds
<> wrote:
> On Wed, Oct 4, 2017 at 10:08 AM, Linus Torvalds
> <> wrote:
>> So I honestly doubt the value of kptr_restrict. Any *sane* policy
>> pretty much has to be in the caller, and by thinking about what you
>> print out. IOW, things like proc_pid_wchan().
> Looking at /proc/kallsyms is actually a prime example of this.
> IOW, the old "open /proc/kallsyms as a normal user, then make it stdin
> for some suid-root program that can be fooled to output it probably
> works on it.

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.

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