Re: [PATCH net v2] net: bgmac: fix oversized RX frame check

[Rosen Penev]

On Tue, Oct 27, 2026 at 7:21 PM Chenguang Zhao <chenguang.zhao@xxxxxxxxx> wrote:
>
> On Tue, Oct 27, 2026 at 06:10:35PM -0700, Rosen Penev wrote:
> > While reviewing commit 77dac783f11
> > ("net: bgmac: rate limit RX error messages") , Florian spotted that the RX
> > length sanity check compares the length reported in the RX header against
> > BGMAC_RX_ALLOC_SIZE. That is the size of the whole fragment, including the
> > space reserved for struct skb_shared_info. The data area handed to the
> > hardware is only BGMAC_RX_BUF_SIZE bytes, and the frame starts
> > BGMAC_RX_FRAME_OFFSET bytes into it, so a valid frame is at most
> > BGMAC_RX_MAX_FRAME_SIZE bytes long.
> >
> > A corrupted length between those two limits passes the check, and the
> > following skb_put() runs past the skb tailroom and calls
> > skb_over_panic() instead of dropping the frame.
> >
> > Compare against BGMAC_RX_MAX_FRAME_SIZE instead.
> >
> > Only compile tested. Not tested on hardware.
> >
> > Fixes: 6a6c708469c9 ("bgmac: add check for oversized packets")
> > Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> > ---
> >  v2: replace Suggested-by with description.
> >  drivers/net/ethernet/broadcom/bgmac.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
> > index b3a92ae95de3..6873c7bb7a14 100644
> > --- a/drivers/net/ethernet/broadcom/bgmac.c
> > +++ b/drivers/net/ethernet/broadcom/bgmac.c
> > @@ -455,7 +455,7 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
> >                               break;
> >                       }
> >
> > -                     if (len > BGMAC_RX_ALLOC_SIZE) {
> > +                     if (len > BGMAC_RX_MAX_FRAME_SIZE) {
> >                               if (net_ratelimit())
> >                                       netdev_err(bgmac->net_dev, "Found oversized packet at slot %d, DMA issue!\n",
> >                                                  ring->start);
> > --
> > 2.56.0
> >
>
> Hi Rosen
>
> FWIW, it’s helpful for reviewers to have a link to the
> prior patch with the new revision for easy reference. :)
https://lore.kernel.org/netdev/20261023005313.3946390-1-rosenp@xxxxxxxxx/
>
> Thanks
> Chenguang