netdev - Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement fast refcount overflow protection

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Date:   Thu, 31 Aug 2017 12:28:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mike Galbraith <efault@....de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement
 fast refcount overflow protection

On Thu, Aug 31, 2017 at 6:58 AM, Mike Galbraith <efault@....de> wrote:
> gdb) list *in6_dev_get+0x10
> 0xffffffff8166d3d0 is in in6_dev_get (./include/net/addrconf.h:318).
> 313     {
> 314             struct inet6_dev *idev;
> 315
> 316             rcu_read_lock();
> 317             idev = rcu_dereference(dev->ip6_ptr);
> 318             if (idev)
> 319                     refcount_inc(&idev->refcnt);
> 320             rcu_read_unlock();
> 321             return idev;
> 322

And this is a completely different refcount from the other that
tripped. This one is quite simple, too, though I see it uses
refcount_dec(), which is a path to saturation. I've sent a patch to
try to clarify this further...

-Kees

-- 
Kees Cook
Pixel Security