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Message-ID: <CAPDLWs8jyL3W_sGmHtw4Uw=8U_OYfeWJd_BpBLE7zvO4c6Z_8g@mail.gmail.com>
Date: Thu, 9 Nov 2017 10:13:26 +0530
From: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Laura Abbott <labbott@...hat.com>, "Tobin C. Harding" <me@...in.cc>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"Jason A. Donenfeld" <Jason@...c4.com>, "Theodore Ts'o" <tytso@....edu>, Kees Cook <keescook@...omium.org>,
Paolo Bonzini <pbonzini@...hat.com>, Tycho Andersen <tycho@...ker.com>,
"Roberts, William C" <william.c.roberts@...el.com>, Tejun Heo <tj@...nel.org>,
Jordan Glover <Golden_Miller83@...tonmail.ch>, Greg KH <gregkh@...uxfoundation.org>,
Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>,
Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>,
Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Network Development <netdev@...r.kernel.org>,
David Miller <davem@...emloft.net>
Subject: Re: [PATCH v4] scripts: add leaking_addresses.pl
> 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 System.map?
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).
Indeed.
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