[PATCH net] bng_en: pad short frames before sampling nr_frags

[Eric Dumazet <edumazet@kernel.org>]

bnge_start_xmit() samples skb_shinfo(skb)->nr_frags into last_frag,
and stores it in tx_buf->nr_frags, before calling eth_skb_pad().

If a nonlinear skb is shorter than ETH_ZLEN, __skb_pad() calls
skb_linearize(), which pulls the frags into the linear part,
releases the frag pages and sets nr_frags to zero.

bnge_start_xmit() then uses the stale last_frag to fill TX_BD_CNT()
and to walk skb_shinfo(skb)->frags[], DMA-mapping pages the skb
no longer holds a reference on, and sending their content twice.

Fix this by calling eth_skb_pad() before nr_frags is sampled.

Found by Sashiko while reviewing the similar bnxt_en fix.

Fixes: bd5ad9c052c8 ("bng_en: Add TX support")
Link: https://lore.kernel.org/netdev/179134695789.434549.53526916334276884@kernel.org/
Signed-off-by: Eric Dumazet <edumazet@kernel.org>
---
Cc: Vikas Gupta <vikas.gupta@broadcom.com>
Cc: Michael Chan <michael.chan@broadcom.com>
Cc: Pavan Chebbi <pavan.chebbi@broadcom.com>
---
 drivers/net/ethernet/broadcom/bnge/bnge_txrx.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnge/bnge_txrx.c b/drivers/net/ethernet/broadcom/bnge/bnge_txrx.c
index 7d45e057f2e82069b3b54936a02e4c955b2787c8..472b02cc43b3c1174e061906b730c0edf9478846 100644
--- a/drivers/net/ethernet/broadcom/bnge/bnge_txrx.c
+++ b/drivers/net/ethernet/broadcom/bnge/bnge_txrx.c
@@ -1490,6 +1490,9 @@ netdev_tx_t bnge_start_xmit(struct sk_buff *skb, struct net_device *dev)
 			return NETDEV_TX_BUSY;
 	}
 
+	if (eth_skb_pad(skb))
+		goto tx_kick_pending;
+
 	last_frag = skb_shinfo(skb)->nr_frags;
 
 	txbd = &txr->tx_desc_ring[TX_RING(bn, prod)][TX_IDX(prod)];
@@ -1513,9 +1516,6 @@ netdev_tx_t bnge_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (unlikely(skb->no_fcs))
 		lflags |= cpu_to_le32(TX_BD_FLAGS_NO_CRC);
 
-	if (eth_skb_pad(skb))
-		goto tx_kick_pending;
-
 	len = skb_headlen(skb);
 
 	mapping = dma_map_single(bd->dev, skb->data, len, DMA_TO_DEVICE);
-- 
2.53.0