netdev - Re: [PATCH net-next] net: bcmgenet: Add a check for oversized packets

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Date:   Tue, 31 Jan 2023 10:16:15 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Florian Fainelli <florian.fainelli@...adcom.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        maxime@...no.tech, Doug Berger <opendmb@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: bcmgenet: Add a check for oversized packets

On Mon, Jan 30, 2023 at 10:19:07AM -0800, Florian Fainelli wrote:
> On 1/30/23 02:09, Leon Romanovsky wrote:
> > On Sun, Jan 29, 2023 at 01:17:43PM -0800, Florian Fainelli wrote:
> > > 
> > > 
> > > On 1/29/2023 1:42 AM, Leon Romanovsky wrote:
> > > > On Thu, Jan 26, 2023 at 04:08:19PM -0800, Florian Fainelli wrote:
> > > > > Occasionnaly we may get oversized packets from the hardware which
> > > > > exceed the nomimal 2KiB buffer size we allocate SKBs with. Add an early
> > > > > check which drops the packet to avoid invoking skb_over_panic() and move
> > > > > on to processing the next packet.
> > > > > 
> > > > > Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> > > > > ---
> > > > >    drivers/net/ethernet/broadcom/genet/bcmgenet.c | 8 ++++++++
> > > > >    1 file changed, 8 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> > > > > index 21973046b12b..d937daa8ee88 100644
> > > > > --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> > > > > +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> > > > > @@ -2316,6 +2316,14 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
> > > > >    			  __func__, p_index, ring->c_index,
> > > > >    			  ring->read_ptr, dma_length_status);
> > > > > +		if (unlikely(len > RX_BUF_LENGTH)) {
> > > > > +			netif_err(priv, rx_status, dev, "oversized packet\n");
> > > > 
> > > > I don't think that it is wise move to print to dmesg something that can
> > > > be triggered by user over network.
> > > 
> > > A frame larger than RX_BUF_LENGTH intentionally received would be segmented
> > > by the MAC, we have seen this happen however while playing with unsafe clock
> > > ratios for instance or when there are insufficient credits given to the
> > > Ethernet MAC to write frames into DRAM. The print is consistent with other
> > > errors that are captured and is only enabled if the appropriate ethtool
> > > message level bitmask is set.
> > 
> > I saw other prints in that function, but you add new one.
> > Won't netif_err() be printed by default in almost all distro?
> 
> Do distributions alter the drive default message level:
> 
>   #define GENET_MSG_DEFAULT       (NETIF_MSG_DRV | NETIF_MSG_PROBE | \
>                                   NETIF_MSG_LINK)
> ?

Ohh, I didn't know about per-driver defaults.

Thanks for the explanation.

> -- 
> Florian
>