linux-kernel - Re: linux-next: Tree for Jan 20 -- Kernel panic

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Message-ID: <20150121173810.GP29656@ZenIV.linux.org.uk>
Date:	Wed, 21 Jan 2015 17:38:10 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Paul Moore <pmoore@...hat.com>
Cc:	Sabrina Dubroca <sd@...asysnail.net>,
	Thierry Reding <thierry.reding@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-audit@...hat.com,
	Richard Guy Briggs <rgb@...hat.com>
Subject: Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount
 root fs

On Wed, Jan 21, 2015 at 11:16:23AM -0500, Paul Moore wrote:
> On Wednesday, January 21, 2015 04:54:07 PM Sabrina Dubroca wrote:
> > 2015-01-21, 16:39:12 +0100, Thierry Reding wrote:
> > > That doesn't seem to help, at least in my case.
> > 
> > Same here.
> 
> Okay, thanks for trying.  Sorry that didn't resolve things.
> 
> > Well, it's probably not an audit issue.  I tried audit=0 on the
> > commandline, and I just rebuilt a kernel with CONFIG_AUDIT=n, and it's
> > still panicing.  This should have fixed any audit-related issue,
> > right?
> 
> Most likely.  Back to the code I go ...

FWIW, I really wonder if populate_rootfs() (run ultimately from
kernel_init(), by way of kernel_init_freeable(), do_basic_setup() and
do_initcalls()) ends up with some side effects as far as struct filename
are concerned...

Note that if we _ever_ hit reuse logics there, we are going to get bogus
matches asoddingplenty - *all* those sys_mkdir(), etc. are going to be
with filenames in the same reused buffer.  So if anything in there leaks
from one call to another, we are going to have a mess on hands.

Another place where that can be a problem is devtmpfs - there's a kernel
thread doing actual mkdir, mknod, etc. in that abomination and if _that_
ends up accumulating aushit entries, we'll end up with interesting problems.

Folks, could you print the value of audit_dummy_context() in populate_rootfs()
and in drivers/base/devtmpfs.c:devtmpfsd()?
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