On Tue, 16 Mar 2021 11:52:43 -0700 Shannon Nelson wrote:
> We were linearizing non-TSO skbs that had too many frags, but
> we weren't checking number of frags on TSO skbs. This could
> lead to a bad page reference when we received a TSO skb with
> more frags than the Tx descriptor could support.
>
> Fixes: 0f3154e6bcb3 ("ionic: Add Tx and Rx handling")
> Signed-off-by: Shannon Nelson <snel...@pensando.io>
> ---
> .../net/ethernet/pensando/ionic/ionic_txrx.c | 28 ++++++++++---------
> 1 file changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> index 162a1ff1e9d2..462b0d106be4 100644
> --- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> +++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> @@ -1079,25 +1079,27 @@ static int ionic_tx_descs_needed(struct ionic_queue
> *q, struct sk_buff *skb)
> {
> int sg_elems = q->lif->qtype_info[IONIC_QTYPE_TXQ].max_sg_elems;
> struct ionic_tx_stats *stats = q_to_tx_stats(q);
> + int ndescs;
> int err;
>
> - /* If TSO, need roundup(skb->len/mss) descs */
> + /* If TSO, need roundup(skb->len/mss) descs
> + * If non-TSO, just need 1 desc and nr_frags sg elems
> + */
> if (skb_is_gso(skb))
> - return (skb->len / skb_shinfo(skb)->gso_size) + 1;
> + ndescs = (skb->len / skb_shinfo(skb)->gso_size) + 1;
Slightly unrelated but why not gso_segs? len / gso_size + 1 could be
over counting, not to mention that div is expensive.
Are you segmenting in the driver? Why do you need #segs descriptors?
> + else
> + ndescs = 1;
>
> - /* If non-TSO, just need 1 desc and nr_frags sg elems */
> - if (skb_shinfo(skb)->nr_frags <= sg_elems)
> - return 1;
> + /* If too many frags, linearize */
> + if (skb_shinfo(skb)->nr_frags > sg_elems) {
> + err = skb_linearize(skb);
> + if (err)
> + return err;
>
> - /* Too many frags, so linearize */
> - err = skb_linearize(skb);
> - if (err)
> - return err;
> -
> - stats->linearize++;
> + stats->linearize++;
> + }
>
> - /* Need 1 desc and zero sg elems */
> - return 1;
> + return ndescs;
I'd be tempted to push back on the refactoring here, you could've
just replaced return 1;s with return ndescs;s without changing
the indentation.. this will give all backporters a pause. But
not the end of the world, I guess.
> }
>
> static int ionic_maybe_stop_tx(struct ionic_queue *q, int ndescs)
