linux-kernel - Re: commit

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Date:	Fri, 1 Mar 2013 01:07:32 -0500
From:	Dave Jones <davej@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>, dhowells@...hat.com,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: commit_creds oops

On Thu, Feb 28, 2013 at 04:25:40PM -0800, Eric W. Biederman wrote:
 
 > > [   89.639850] RIP: 0010:[<ffffffff810784b0>]  [<ffffffff810784b0>] commit_creds+0x250/0x2f0
 > > [   89.658399] Call Trace:
 > > [   89.658822]  [<ffffffff812c7d9b>] key_change_session_keyring+0xfb/0x140
 > > [   89.659845]  [<ffffffff8106c665>] task_work_run+0xa5/0xd0
 > > [   89.660698]  [<ffffffff81002911>] do_notify_resume+0x71/0xb0
 > > [   89.661581]  [<ffffffff816c9a4a>] int_signal+0x12/0x17
 > >
 > > Appears to be..
 > >
 > >                 if ((set_ns == subset_ns->parent)  &&
 > >      850:       48 8b 8a c8 00 00 00    mov    0xc8(%rdx),%rcx
 > >
 > > from the inlined cred_cap_issubset
 > 
 > Interesting.  That line is protected with the check subset_ns !=
 > &init_user_ns so subset_ns->parent must be valid or subset_ns is not
 > a proper user namespace.
 > 
 > Ugh.  I think I see what is going on and it is just silly. 
 > 
 > It looks like by historical accident we have been reading trying to set
 > new->user_ns from new->user_ns.  Which is totally silly as new->user_ns
 > is NULL (as is every other field in new except session_keyring at that
 > point).
 > 
 > It looks like it is safe to sleep in key_change_session_keyring so why
 > we just don't use prepare_creds there like everywhere else is beyond
 > me.
 > 
 > The intent is clearly to copy all of the fields from old to new so what
 > we should be doing is is copying old->user_ns into new->user_ns.
 > 
 > Dave can you verify that this patch fixes the oops?

Looks like it.  Haven't hit the same thing since applying your patch.

I noticed though that get_user_ns bumps a refcount.  Is this what we
want if we're just copying ?

	Dave

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