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From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Garrett <matthewgarrett@google.com>,
	James Morris James Morris <jmorris@namei.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Ben Hutchings <ben@decadent.org.uk>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 1/7 v2] tracefs: Revert ccbd54ff54e8 ("tracefs: Restrict tracefs when the kernel is locked down")
Date: Sat, 12 Oct 2019 20:39:22 -0400
Message-ID: <20191012203922.3f29b258@gandalf.local.home> (raw)
In-Reply-To: <20191012203502.065258d2@gandalf.local.home>

On Sat, 12 Oct 2019 20:35:02 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sat, 12 Oct 2019 15:56:15 -0700
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> > On Fri, Oct 11, 2019 at 5:59 PM Steven Rostedt <rostedt@goodmis.org> wrote:  
> > >
> > >
> > > I bisected this down to the addition of the proxy_ops into tracefs for
> > > lockdown. It appears that the allocation of the proxy_ops and then freeing
> > > it in the destroy_inode callback, is causing havoc with the memory system.
> > > Reading the documentation about destroy_inode and talking with Linus about
> > > this, this is buggy and wrong.    
> > 
> > Can you still add the explanation about the inode memory leak to this message?
> > 
> > Right now it just says "it's buggy and wrong". True. But doesn't
> > explain _why_ it is buggy and wrong.
> >   
> 
> Sure. The patches just finished my testing (along with other fixes that
> I need to send you). I have to make a few other updates in the change
> log though, so I'll be rebasing them (but not touching the code), to
> clean up the change logs.
> 

I updated this change log to state:

"I bisected this down to the addition of the proxy_ops into tracefs for
lockdown. It appears that the allocation of the proxy_ops and then freeing
it in the destroy_inode callback, is causing havoc with the memory system.
Reading the documentation about destroy_inode and talking with Linus about
this, this is buggy and wrong. When defining the destroy_inode() method, it 
is expected that the destroy_inode() will also free the inode, and not just 
the extra allocations done in the creation of the inode. The faulty commit 
causes a memory leak of the inode data structure when they are deleted."

-- Steve

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-12  0:57 [PATCH 0/7 v2] tracing: Fix tracefs lockdown and various clean ups Steven Rostedt
2019-10-12  0:57 ` [PATCH 1/7 v2] tracefs: Revert ccbd54ff54e8 ("tracefs: Restrict tracefs when the kernel is locked down") Steven Rostedt
2019-10-12 22:56   ` Linus Torvalds
2019-10-13  0:35     ` Steven Rostedt
2019-10-13  0:39       ` Steven Rostedt [this message]
2019-10-12  0:57 ` [PATCH 2/7 v2] ftrace: Get a reference counter for the trace_array on filter files Steven Rostedt
2019-10-12  0:57 ` [PATCH 3/7 v2] tracing: Get trace_array reference for available_tracers files Steven Rostedt
2019-10-12  0:57 ` [PATCH 4/7 v2] tracing: Have trace events system open call tracing_open_generic_tr() Steven Rostedt
2019-10-12  2:09   ` Steven Rostedt
2019-10-12  0:57 ` [PATCH 5/7 v2] tracing: Add tracing_check_open_get_tr() Steven Rostedt
2019-10-12  0:57 ` [PATCH 6/7 v2] tracing: Add some more locked_down checks Steven Rostedt
2019-10-12  0:57 ` [PATCH 7/7 v2] tracing: Do not create tracefs files if tracefs lockdown is in effect Steven Rostedt

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