GPF when doing jail -r, possibly an use-after-free

Bjoern A. Zeeb bzeeb-lists at
Mon Jul 9 06:07:08 UTC 2012

On 9. Jul 2012, at 06:01 , Mikolaj Golub wrote:

> On Sun, 8 Jul 2012 20:52:55 +0000 Bjoern A. Zeeb wrote:
> BAZ> Situation 1)
> BAZ>         epairNa is in base, eiparNb is jail foo
> BAZ>         stop jail foo: jail -r foo
> BAZ>         both epairN[ab] will live in base and can be destiryed without vnet switching
> BAZ> Situation 2)
> BAZ>         epairNa is in base, eiparNb is jail foo
> BAZ>         you are in jail foo and type epairNb destroy;  that should not be allowed
> BAZ> Situation 3)
> BAZ>         epairNa is in base, eiparNb is jail foo
> BAZ>         you are in base and type ifconfig epairNa destroy
> BAZ>         This is your case ...  I am not sure what I'd expect in this case,
> BAZ>         especailly given epair is special...  You probably are right.
> BAZ>         Ideally I'd not allow it to be destroyed unless both are in the
> BAZ>         if_home_vnet.  However it seems we allow this; so in that case
> BAZ>         I definitively make sure to use the CURVNET_SET_QUIET() version
> BAZ>         to avoid the expected noise otherwise.
> It looks like epair was expected to allow this, because in non-patched version
> it already did switching before freeing the interface. It just did not switch
> bere detaching.
> CURVNET_SET_QUIET() is used in the current version of the patch so I suppose I
> can commit it.
> But if you think that just not allowing to destroy unless both ends are in the
> f_home_vnet is a preferred solution and it is not late to change this I can
> provide the patch.

Get it in for now; it helps people.  We should keep the other things in mind and
write down a proper policy; it's more interesting as you can do other things with
cloners you can create inside a vnet as well, today and later.

> BAZ> The moment cloners will handle this it'll all be centrally managed
> BAZ> and individual device drivers shouldn't need to worry about it anymore.
> -- 
> Mikolaj Golub
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Bjoern A. Zeeb                                 You have to have visions!
   It does not matter how good you are. It matters what good you do!

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