linux-kernel - Re: [RFC][PATCH 1/1] support for user-space buffers in kfifo

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Date:	Tue, 12 Jun 2007 15:43:01 +0200
From:	Stelian Pop <stelian@...ies.net>
To:	Nelson Castillo <nelsoneci@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/1] support for user-space buffers in kfifo

Le lundi 11 juin 2007 à 16:26 -0500, Nelson Castillo a écrit :
> Hi.
> 
> I just added support for user space buffers in kfifo. I found useful
> __kfifo_get_user to copy data to a user buffer in a read call. I didn't
> like the idea of having an extra buffer.
> 
> * Is it ok to add this support?

I suppose it is, however:

> +	spin_lock_irqsave(fifo->lock, flags);
> +
> +	ret = __kfifo_put_user(fifo, buffer, len);
> +
> +	spin_unlock_irqrestore(fifo->lock, flags);
[...]

> +int __kfifo_put_user(struct kfifo *fifo, const unsigned char __user *buffer,
> +	        unsigned int len)
[...]

> +	if(copy_from_user(fifo->buffer + (fifo->in & (fifo->size - 1)),
> +			  buffer, l))
> +		return  -EFAULT;
[...]

accessing userspace memory with a spinlock taken (moreover an irqsave()
one) is bad bad bad.

Stelian.
-- 
Stelian Pop <stelian@...ies.net>

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