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

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Date:	Tue, 08 Aug 2006 14:43:38 +0400
From:	Kirill Korotaev <dev@...ru>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] unserialized task->files changing

Eric Dumazet wrote:
> 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() ?

yeah, never do assignments in declarations :)

BTW, not sure about kthread_exit_files() yet, but looks like it suffers too.

unshare_files() changes current->files w/o locking as well. but I can't see
where it puts the old files... hmm...

Kirill
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