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Date: Thu, 9 Nov 2017 10:13:26 +0530
From: Kaiwan N Billimoria <>
To: Linus Torvalds <>
Cc: Laura Abbott <>, "Tobin C. Harding" <>, 
	"" <>, 
	"Jason A. Donenfeld" <>, "Theodore Ts'o" <>, Kees Cook <>, 
	Paolo Bonzini <>, Tycho Andersen <>, 
	"Roberts, William C" <>, Tejun Heo <>, 
	Jordan Glover <>, Greg KH <>, 
	Petr Mladek <>, Joe Perches <>, Ian Campbell <>, 
	Sergey Senozhatsky <>, Catalin Marinas <>, 
	Will Deacon <>, Steven Rostedt <>, 
	Chris Fries <>, Dave Weinstein <>, 
	Daniel Micay <>, Djalal Harouni <>, 
	Linux Kernel Mailing List <>, Network Development <>, 
	David Miller <>
Subject: Re: [PATCH v4] scripts: add

> But I don't know if there is anything else than the profiling code
> that _really_ wants access to /proc/kallsyms in user space as a
> regular user.

Am unsure about this, but kprobes? (/jprobes/kretprobes), and by
extension, wrappers over this infra (like SystemTap)?
I (hazily) recollect a script I once wrote (years back though) that
collects kernel virtual addresses off of kallsyms for the purpose of
passing them to a 'helper' kernel module that uses kprobes. I realize
that 'modern' kprobes exposes APIs that just require the symbolic name
& that they're anyway at kernel privilege... but the point is, a
usermode script was picking up and passing the kernel addresses.

Also, what about kernel addresses exposed via
Oh, just checked, it's root rw only.. pl ignore.

> That said, that patch also fixes the /proc/kallsyms root check, in
> that now you can do:
>     sudo head < /proc/kallsyms
> and it still shows all zeroes - because the file was *opened* as a
> normal user. That's how UNIX file access security works, and how it is
> fundamentally supposed to work (ie passing a file descriptor to a sui
> program doesn't magically make it gain privileges).


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