Re: [PATCH net] net: wwan: t7xx: off-by-one error in t7xx_dpmaif_rx_buf_alloc()

[Ilpo Järvinen]

On Tue, 29 Oct 2024, Sergey Ryazanov wrote:

> Hello Jinjie,
> 
> On 28.10.2024 10:06, Jinjie Ruan wrote:
> > The error path in t7xx_dpmaif_rx_buf_alloc(), free and unmap the already
> > allocated and mapped skb in a loop, but the loop condition terminates when
> > the index reaches zero, which fails to free the first allocated skb at
> > index zero.
> > 
> > Check for >= 0 so that skb at index 0 is freed as well.
> 
> Nice catch! Still implementation needs some improvements, see below.
> 
> > 
> > Fixes: d642b012df70 ("net: wwan: t7xx: Add data path interface")
> > Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> > ---
> >   drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> > b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> > index 210d84c67ef9..f2298330e05b 100644
> > --- a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> > +++ b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> > @@ -226,7 +226,7 @@ int t7xx_dpmaif_rx_buf_alloc(struct dpmaif_ctrl
> > *dpmaif_ctrl,
> >   	return 0;
> >     err_unmap_skbs:
> > -	while (--i > 0)
> > +	while (--i >= 0)
> >   		t7xx_unmap_bat_skb(dpmaif_ctrl->dev, bat_req->bat_skb, i);
> 
> The index variable declared as unsigned so changing the condition alone will
> cause the endless loop. Can you change the variable type to signed as well?

Isn't the usual pattern:

	while (i--)
		t7xx_unmap_bat_skb(dpmaif_ctrl->dev, bat_req->bat_skb, i);

?

-- 
 i.