[PATCH] rtase: fix double free of multi-frag skb on DMA map failure

[Yun Lu <luyun_611@163.com>]

From: Yun Lu <luyun@kylinos.cn>

In rtase_start_xmit(), when the head buffer DMA mapping fails after
rtase_xmit_frags() has mapped all fragments, the error path clears
the fragment descriptors with rtase_tx_clear_range(), which frees
the skb through the last-frag slot and accounts tx_dropped. Control
then falls through to the common error label, which frees the same
skb a second time and counts it again.

Return right after clearing the fragments when the skb owns frags;
the no-frag case still drops through and frees the head skb once.

Fixes: d6e882b89fdf ("rtase: Implement .ndo_start_xmit function")
Signed-off-by: Yun Lu <luyun@kylinos.cn>
---
 drivers/net/ethernet/realtek/rtase/rtase_main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/realtek/rtase/rtase_main.c b/drivers/net/ethernet/realtek/rtase/rtase_main.c
index 255667775f0e..67f7fdada119 100644
--- a/drivers/net/ethernet/realtek/rtase/rtase_main.c
+++ b/drivers/net/ethernet/realtek/rtase/rtase_main.c
@@ -1426,6 +1426,9 @@ static netdev_tx_t rtase_start_xmit(struct sk_buff *skb,
 err_dma_1:
 	ring->skbuff[entry] = NULL;
 	rtase_tx_clear_range(ring, ring->cur_idx + 1, frags);
+	if (frags)
+		/* the frags were cleared above, along with the skb */
+		return NETDEV_TX_OK;
 
 err_dma_0:
 	tp->stats.tx_dropped++;
-- 
2.43.0