netdev - Re: selinux networking: sleeping functin called from invalid context in 2.6.20-rc[12]

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Message-ID: <20070102155826.A14811@freya>
Date:	Tue, 2 Jan 2007 15:58:26 +0800
From:	"Adam J. Richter" <adam@...drasil.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Paul Moore <paul.moore@...com>
Subject: Re: selinux networking: sleeping functin called from invalid context in 2.6.20-rc[12]

On Sun, Dec 24, 2006 at 04:25:11PM -0800, Andrew Morton wrote:
> On Mon, 25 Dec 2006 05:21:24 +0800
> "Adam J. Richter" <adam@...drasil.com> wrote:
> 
>> 	Under 2.6.20-rc1 and 2.6.20-rc2, I get the following complaint
>> for several network programs running on my system:
>> 
>> [  156.381868] BUG: sleeping function called from invalid context at net/core/sock.c:1523
[...]
> There's a glaring bug in selinux_netlbl_inode_permission() - taking
> lock_sock() inside rcu_read_lock().
> 
> I would again draw attention to Documentation/SubmitChecklist.  In
> particular please always always always enable all kernel debugging options
> when developing and testing new kernel code.  And everything else in that
> file, too.
> 
> <guesses that this was tested on ia64>

	I have not yet performed the 21 steps of
linux-2.6.20-rc3/Documentation/SubmitChecklist, which I think is a
great objectives list for future automation or some kind of community
web site.  I hope to find time to make progress through that
checklist, but, in the meantime, I think the world may nevertheless be
infinitesmally better off if I post the patch that I'm currently
using that seems to fix the problem, seeing as how rc3 has passed
with no fix incorporated.

	I think the intent of the offending code was to avoid doing
a lock_sock() in a presumably common case where there was no need to
take the lock.  So, I have kept the presumably fast test to exit
early.

	When it turns out to be necessary to take lock_sock(), RCU is
unlocked, then lock_sock is taken, the RCU is locked again, and
the test is repeated.

	If I am wrong about lock_sock being expensive, I can
delete the lines that do the early return.

	By the way, in a change not included in this patch,
I also tried consolidating the RCU locking in this file into a macro
IF_NLBL_REQUIRE(sksec, action), where "action" is the code
fragment to be executed with rcu_read_lock() held, although this
required splitting a couple of functions in half.

	Anyhow, here is my current patch as MIME attachment.
Comments and labor in getting it through SubmitChecklist would
both be welcome.

Adam Richter

View attachment "selinux.diff" of type "text/plain" (622 bytes)