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

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Message-ID: <2accc2ff0706120755sf0176e6yc55e65ec0502da5b@mail.gmail.com>
Date:	Tue, 12 Jun 2007 09:55:17 -0500
From:	"Nelson Castillo" <nelsoneci@...il.com>
To:	"Stelian Pop" <stelian@...ies.net>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/1] support for user-space buffers in kfifo

On 6/12/07, Stelian Pop <stelian@...ies.net> wrote:
> 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.

Yes.

Perhaps then only the functions __kfifo_put_user and __kfifo_get_user should
be allowed. Those are the ones I'm using now , anyway.
I added the others for completeness but adding them is probably a mistake.

Regards,
Nelson.-

-- 
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