RE: [PATCH net] ravb: Fix potential use-after-free in ravb_rx_gbeth()

[Biju Das]

Hi Geert,

> Subject: Re: [PATCH net] ravb: Fix potential use-after-free in
> ravb_rx_gbeth()
> 
> Hi Biju,
> 
> On Sat, Dec 3, 2022 at 11:29 AM Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> wrote:
> > > Subject: [PATCH net] ravb: Fix potential use-after-free in
> > > ravb_rx_gbeth()
> > >
> > > The skb is delivered to napi_gro_receive() which may free it, after
> > > calling this, dereferencing skb may trigger use-after-free.
> >
> > Can you please reconfirm the changes you have done is actually fixing
> any issue?
> > If yes, please provide the details.
> >
> > Current code,
> >
> > napi_gro_receive(&priv->napi[q], priv->rx_1st_skb);
> 
> IIUIC, after this, priv->rx_1st_skb may have been freed...
> 
> >
> > - stats->rx_bytes += priv->rx_1st_skb->len;
> 
> ... so accessing priv->rx_1st_skb->len here may be a UAF.
> 
> > + stats->rx_bytes += pkt_len;
> 
> So this change looks correct to me, as pkt_len was stored to
> priv->rx_1st_skb->len using skb_put() before.

Thanks for detailed explanation. It makes sense now.

Cheers,
Biju
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> 
> >
> > Note: I haven't tested your patch yet to see it cause any regression.
> >
> > Cheers,
> > Biju
> >
> > >
> > > Fixes: 1c59eb678cbd ("ravb: Fillup ravb_rx_gbeth() stub")
> > > Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
> > > ---
> > >  drivers/net/ethernet/renesas/ravb_main.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/ethernet/renesas/ravb_main.c
> > > b/drivers/net/ethernet/renesas/ravb_main.c
> > > index 6bc923326268..33f723a9f471 100644
> > > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > > @@ -841,7 +841,7 @@ static bool ravb_rx_gbeth(struct net_device
> > > *ndev, int *quota, int q)
> > >                               napi_gro_receive(&priv->napi[q],
> > >                                                priv->rx_1st_skb);
> > >                               stats->rx_packets++;
> > > -                             stats->rx_bytes += priv->rx_1st_skb-
> >len;
> > > +                             stats->rx_bytes += pkt_len;
> > >                               break;
> > >                       }
> > >               }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
> But when I'm talking to journalists I just say "programmer" or something
> like that.
>                                 -- Linus Torvalds