Re: [PATCH v4 1/5] mfd: Add support for Intel LJCA device

Ye, Xiang
2023-03-14T07:15:23Z

Hi Oliver,

Thanks for the review.
On Mon, Mar 13, 2023 at 02:27:50PM +0100, Oliver Neukum wrote:
> On 10.03.23 05:14, Ye, Xiang wrote:
> > Hi Oliver,
>
> Hi,
>
> sorry for the delayed answer.
No problem.
>
> > Thanks for your review.
> > On Thu, Mar 09, 2023 at 01:53:28PM +0100, Oliver Neukum wrote:
> > >
> > >
> > > On 09.03.23 08:10, Ye Xiang wrote:
> > >
> > > > +static int ljca_stub_write(struct ljca_stub *stub, u8 cmd, const void *obuf, unsigned int obuf_len,
> > > > + void *ibuf, unsigned int *ibuf_len, bool wait_ack, unsigned long timeout)
> > >
> > > Why do you make ibuf_len a pointer?
> > Because ibuf_len is also used as output of this function here.
> > It stores the actual length of ibuf receive from LJCA device.
>
> Yes, I understand that now, thank you for the explanation, yet
> that is problematic, if we look at another issue. See further down:
>
> > > > + ret = -ENODEV;
> > > > + goto error_put;
> > > > + }
> > > > +
> > > > + mutex_lock(&dev->mutex);
> > > > + stub->cur_cmd = cmd;
> > > > + stub->ipacket.ibuf = ibuf;
> > > > + stub->ipacket.ibuf_len = ibuf_len;
>
> Here you store the pointer into the stub. Hence we must make sure
> that the location it points to stays valid.
>

> Now let's look at ljca_mng_reset_handshake(). I am afraid I have to quote
> its first part in full:
>
> +static int ljca_mng_reset_handshake(struct ljca_stub *stub)
> +{
> + struct ljca_mng_priv *priv;
> + __le32 reset_id;
> + __le32 reset_id_ret = 0;
> + unsigned int ilen = sizeof(__le32);
>
> This is on the _stack_
> Highly important !!!
>
> + int ret;
> +
> + priv = ljca_priv(stub);
> + reset_id = cpu_to_le32(priv->reset_id++);
> + ret = ljca_stub_write(stub, LJCA_MNG_RESET_NOTIFY, &reset_id, sizeof(reset_id),
> + &reset_id_ret, &ilen, true, LJCA_USB_WRITE_ACK_TIMEOUT_MS);
>
> If we run into the timeout error case, ret will be -ETIMEDOUT.
>
> + if (ret)
> + return ret;
>
> And thus here we return and free the stack _including_ "ilen", which we
> still have a pointer to. That means if the operation concludes after
> a timeout, we _will_ follow a rogue pointer.
> A couple of functions have this race condition.
Got it. Will fix that on next version.
>
>

Thanks
Ye Xiang