Re: [PATCH net] net: wwan: t7xx: off-by-one error in t7xx_dpmaif_rx_buf_alloc()
From: Ilpo Järvinen
Date: Tue Oct 29 2024 - 06:58:24 EST
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.