Re: [PATCH] unserialized task->files changing

[Kirill Korotaev <dev@sw.ru>]

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