linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 1/26] uprobes: Auxillary routines to insert, find, delete uprobes

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Date:	Mon, 26 Sep 2011 13:18:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 1/26]   uprobes: Auxillary routines to
 insert, find, delete uprobes

On Tue, 2011-09-20 at 16:42 +0100, Stefan Hajnoczi wrote:
> On Tue, Sep 20, 2011 at 05:29:49PM +0530, Srikar Dronamraju wrote:
> > +static void delete_uprobe(struct uprobe *uprobe)
> > +{
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&uprobes_treelock, flags);
> > +	rb_erase(&uprobe->rb_node, &uprobes_tree);
> > +	spin_unlock_irqrestore(&uprobes_treelock, flags);
> > +	put_uprobe(uprobe);
> > +	iput(uprobe->inode);
> 
> Use-after-free when put_uprobe() kfrees() the uprobe?

I suspect the caller still has one, and this was the reference for being
part of the tree. But yes, that could do with a comment.

The comment near atomic_set() in __insert_uprobe() isn't too clear
either. /* get access + drop ref */, would naively seem +1 -1 = 0,
instead of +1 +1 = 2.


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