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

On Tue, Oct 27, 2026 at 7:21 PM Chenguang Zhao [off-list ref] wrote:

On Tue, Oct 27, 2026 at 06:10:35PM -0700, Rosen Penev wrote:

quoted

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 <redacted>
---
 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@gmail.com/ (local)

Thanks
Chenguang