Re: fuzz tested user mode linux core dumps in fs/lockd/clntproc.c:131

[Oleg Nesterov <oleg@redhat.com>]

On 07/28, Toralf Förster wrote:
>
> The attached patch works - applied on top of current git -
> at least the issue cannot be reproduced then.

Thanks Toralf.

I'll write the changelog and send the patch tomorrow.

Andrey, any chance you can check that with this patch free_ipc_ns()
doesn't have any problem with ->shm_file ?

e7b2c406 should be enough to fix that leak, but it would be nice if
you can confirm.

> On 07/27/2013 07:00 PM, Oleg Nesterov wrote:
> > On 07/27, Toralf Förster wrote:
> >>
> >> I do have a user mode linux image (stable 32 bit Gentoo Linux ) which erratically crashes
> >> while fuzz tested with trinity if the victim files are located on a NFS share.
> >>
> >> The back trace of the core dumps always looks like the attached.
> >>
> >> To bisect it is hard. However after few attempts in the last weeks the following
> >> commit is either the first bad commit or at least the upper limit (less likely).
> >>
> >>
> >> commit 8aac62706adaaf0fab02c4327761561c8bda9448
> >> Author: Oleg Nesterov <oleg@redhat.com>
> >> Date:   Fri Jun 14 21:09:49 2013 +0200
> >>
> >>     move exit_task_namespaces() outside of exit_notify()
> >>
> >> #15 nlmclnt_setlockargs (req=0x48e18860, fl=0x48f27c8c) at fs/lockd/clntproc.c:131
> > 
> > Thanks.
> > 
> > So nlmclnt_setlockargs()->utsname() crashes and we probably need
> > the patch below.
> > 
> > But is it correct? I know _absolutely_ nothing about nfs/sunrpc/etc and
> > I never looked into this code before, most probably I am wrong.
> > 
> > But it seems that __nlm_async_call() relies on workqueues.
> > nlmclnt_async_call() does rpc_wait_for_completion_task(), but what if
> > the caller is killed?
> > 
> > nlm_rqst can't go away, ->a_count was incremented. But can't the caller
> > exit before call->name is used? In this case the memory it points to
> > can be already freed.
> > 
> > Oleg.
> > 
> > --- x/kernel/exit.c
> > +++ x/kernel/exit.c
> > @@ -783,8 +783,8 @@ void do_exit(long code)
> >  	exit_shm(tsk);
> >  	exit_files(tsk);
> >  	exit_fs(tsk);
> > -	exit_task_namespaces(tsk);
> >  	exit_task_work(tsk);
> > +	exit_task_namespaces(tsk);
> >  	check_stack_usage();
> >  	exit_thread();
> >  
> > 
> > 
> 
> 
> -- 
> MfG/Sincerely
> Toralf Förster
> pgp finger print: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 7DB6 9DA3