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

[Rosen Penev <rosenp@gmail.com>]

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@gmail.com>
---
 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