Re: [PATCH net] net: vertexcom: mse102x: Fix possible double free of TX skb

[Stefan Wahren]

Am 29.10.24 um 23:01 schrieb Jakub Kicinski:
> On Tue, 29 Oct 2024 22:15:15 +0100 Stefan Wahren wrote:
> > > Isn't it easier to change this function to free the copy rather than
> > > the original? That way the original will remain valid for the callers.
> > You mean something like this?
> >
> > diff --git a/drivers/net/ethernet/vertexcom/mse102x.c
> > b/drivers/net/ethernet/vertexcom/mse102x.c
> > index a04d4073def9..2c37957478fb 100644
> > --- a/drivers/net/ethernet/vertexcom/mse102x.c
> > +++ b/drivers/net/ethernet/vertexcom/mse102x.c
> > @@ -222,7 +222,7 @@ static int mse102x_tx_frame_spi(struct mse102x_net
> > *mse, struct sk_buff *txp,
> >        struct mse102x_net_spi *mses = to_mse102x_spi(mse);
> >        struct spi_transfer *xfer = &mses->spi_xfer;
> >        struct spi_message *msg = &mses->spi_msg;
> > -    struct sk_buff *tskb;
> > +    struct sk_buff *tskb = NULL;
> >        int ret;
> >
> >        netif_dbg(mse, tx_queued, mse->ndev, "%s: skb %p, %d@%p\n",
> > @@ -235,7 +235,6 @@ static int mse102x_tx_frame_spi(struct mse102x_net
> > *mse, struct sk_buff *txp,
> >            if (!tskb)
> >                return -ENOMEM;
> >
> > -        dev_kfree_skb(txp);
> >            txp = tskb;
> >        }
> >
> > @@ -257,6 +256,8 @@ static int mse102x_tx_frame_spi(struct mse102x_net
> > *mse, struct sk_buff *txp,
> >            mse->stats.xfer_err++;
> >        }
> >
> > +    dev_kfree_skb(tskb);
> > +
> >        return ret;
> >    }
> Exactly, I think it would work and it feels simpler.
I didn't test it yet, i need access to evaluation board before. But this
change will behave differently regarding stats of tx_bytes [1]. The
first version will include the padding, while the second does not.

[1] -
https://elixir.bootlin.com/linux/v6.12-rc5/source/drivers/net/ethernet/vertexcom/mse102x.c#L445