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

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Message-ID: <Y9eXb+ZYanvxfq2E@unreal>
Date:   Mon, 30 Jan 2023 12:09:51 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     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 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?

Thanks

> -- 
> Florian