Re: 2.6.17-rc4-mm1

[Tilman Schmidt <tilman@imap.cc>]

On 15.05.2006 20:10, Jesper Juhl wrote:
> In the 
> isdn-unsafe-interaction-between-isdn_write-and-isdn_writebuf_stub.patch 
> patch, which is currently in -mm there's a bug.
> 
> This bit :
>  -       copy_from_user(skb_put(skb, len), buf, len);
>  +       if (!copy_from_user(skb_put(skb, len), buf, len))
> should really be :
>  -       copy_from_user(skb_put(skb, len), buf, len);
>  +       if (copy_from_user(skb_put(skb, len), buf, len))
> Somehow a stray "!" crept in there.

Ouch. I hadn't noticed that either. Sorry about that.

Strangely, I ran a system with that patch for quite some time, actually
doing all kinds of ISDN connections without ever noticing any ill
effects. I can only conclude that the affected codebranch was never
exercised, which makes me suspect it is dead, or at least pining for the
fjords. Looking closer, I can't help noticing that the only branch
calling the affected function isdn_writebuf_stub() starts out with:

	printk(KERN_WARNING "isdn_write minor %d obsolete!\n", minor);

So I guess it really doesn't make much difference one way or the other.
But it's certainly more correct that way, so:

> Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Acked-by: Tilman Schmidt <tilman@imap.cc>

> --- linux-2.6.17-rc4-mm1-orig/drivers/isdn/i4l/isdn_common.c	2006-05-15 19:43:06.000000000 +0200
> +++ linux-2.6.17-rc4-mm1/drivers/isdn/i4l/isdn_common.c	2006-05-15 19:58:26.000000000 +0200
> @@ -1952,7 +1952,7 @@ isdn_writebuf_stub(int drvidx, int chan,
>  	if (!skb)
>  		return -ENOMEM;
>  	skb_reserve(skb, hl);
> -	if (!copy_from_user(skb_put(skb, len), buf, len))
> +	if (copy_from_user(skb_put(skb, len), buf, len))
>  		return -EFAULT;
>  	ret = dev->drv[drvidx]->interface->writebuf_skb(drvidx, chan, 1, skb);
>  	if (ret <= 0)

-- 
Tilman Schmidt                          E-Mail: tilman@imap.cc
Bonn, Germany
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