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

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Message-ID: <20150121153910.GD22884@ulmo.nvidia.com>
Date:	Wed, 21 Jan 2015 16:39:12 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Paul Moore <pmoore@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Sabrina Dubroca <sd@...asysnail.net>,
	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 10:24:11AM -0500, Paul Moore wrote:
> On Wednesday, January 21, 2015 03:42:16 PM Thierry Reding wrote:
> > On Wed, Jan 21, 2015 at 12:05:39PM +0100, Sabrina Dubroca wrote:
> > > 2015-01-21, 04:36:38 +0000, Al Viro wrote:
> > > > On Tue, Jan 20, 2015 at 08:01:26PM -0800, Guenter Roeck wrote:
> > > > > With this patch:
> > > > > 
> > > > > sys_mkdir .:40775 returned -17
> > > > > sys_mkdir usr:40775 returned 0
> > > > > sys_mkdir usr/lib:40775 returned 0
> > > > > sys_mkdir usr/share:40755 returned 0
> > > > > sys_mkdir usr/share/udhcpc:40755 returned 0
> > > > > sys_mkdir usr/bin:40775 returned 0
> > > > > sys_mkdir usr/sbin:40775 returned 0
> > > > > sys_mkdir mnt:40775 returned 0
> > > > > sys_mkdir proc:40775 returned 0
> > > > > sys_mkdir root:40775 returned 0
> > > > > sys_mkdir lib:40775 returned 0
> > > > > sys_mkdir lib/modules:40775 returned 0
> > > > > ...
> > > > > 
> > > > > and the problem is fixed.
> > > 
> > > This patch also works for me.
> > > 
> > > > ... except that it simply confirms that something's fishy with
> > > > getname_kernel() of ->name of struct filename returned by getname(). 
> > > > IOW, I still do not understand the mechanism of breakage there.
> > > 
> > > I'm not so sure about that.  I tried to copy name to a new string in
> > > do_path_lookup and that didn't help.
> > > 
> > > Now, I've removed the
> > > 
> > >         putname(filename);
> > > 
> > > line from do_path_lookup and I don't get the panic.
> > 
> > That would indicate that somehow the refcount got unbalanced. Looking
> > more closely it seems like the various audit_*() function do take a
> > reference, but maybe that's not enough.
> 
> I'm thinking the same thing and I think the problem may be that 
> __audit_reusename() is not bumping the filename->refcnt.  Can someone who is 
> seeing this problem bump the refcnt in __audit_reusename()?
> 
>   struct filename *
>   __audit_reusename(const __user char *uptr)
>   {
>         struct audit_context *context = current->audit_context;
>         struct audit_names *n;
> 
>         list_for_each_entry(n, &context->names_list, list) {
>                 if (!n->name)
>                         continue;
>                 if (n->name->uptr == uptr) {
> +                       n->name->refcnt++;
>                         return n->name;
>                 }
>         }
>         return NULL;
>   }

That doesn't seem to help, at least in my case.

Thierry

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