[PATCH net v1 3/3] net: hibmcge: fix double-free of tx skb on DMA mapping failure

[xuanqiang.luo@linux.dev]

From: Xuanqiang Luo <luoxuanqiang@kylinos.cn>

If hbg_dma_map() fails, hbg_net_start_xmit() frees the skb, but buffer->skb
is left pointing to it. ring->ntu is not advanced, so the buffer is not
visible to the TX cleanup path.

A subsequent transmit normally overwrites the buffer. However, if the
interface is brought down first, hbg_ring_uninit() calls hbg_buffer_free().
It sees the stale pointer, attempts to unmap the failed mapping, and frees
the skb again.

Clear buffer->skb before freeing the skb in the error path, preventing
hbg_buffer_free() from treating it as an outstanding TX buffer.

Fixes: 40735e7543f9 ("net: hibmcge: Implement .ndo_start_xmit function")
Cc: stable@vger.kernel.org
Assisted-by: Opencode:deepseek-v4-pro[1m]
Signed-off-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
---
 drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.c b/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.c
index 0ae3149946769..4382af937e2e7 100644
--- a/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.c
+++ b/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.c
@@ -155,6 +155,7 @@ netdev_tx_t hbg_net_start_xmit(struct sk_buff *skb, struct net_device *netdev)
 	buffer->skb = skb;
 	buffer->skb_len = skb->len;
 	if (unlikely(hbg_dma_map(buffer))) {
+		buffer->skb = NULL;
 		dev_kfree_skb_any(skb);
 		return NETDEV_TX_OK;
 	}
-- 
2.43.0