linux-kernel - Re: [PATCH] unserialized task->files changing

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Date:	Tue, 8 Aug 2006 12:23:09 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Kirill Korotaev <dev@...ru>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] unserialized task->files changing

On Tuesday 08 August 2006 12:12, Christoph Hellwig wrote:
> On Tue, Aug 08, 2006 at 02:07:49PM +0400, Kirill Korotaev wrote:
> > Fixed race on put_files_struct on exec with proc.
> > Restoring files on current on error path may lead
> > to proc having a pointer to already kfree-d files_struct.
>
> This is three times the exact same code sequence, it should probably go
> into a helper:
>
> void reset_current_files(struct files_struct *files)
> {
> 	struct files_struct *old = current->files;
>
> 	task_lock(current);
> 	current->files = files;
> 	task_unlock(current);
> 	put_files_struct(old);
> }


More over I think you want to task_lock() before reading current->files 
into 'old'

task_lock(current);
old = current->files;
current->files = files;
task_unlock(current);
put_files_struct(old);

or maybe a xchg() ?

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