net: renesas: rswitch: fix leaked pointer on error path

[ Upstream commit bb61732 ]

If error path is taken while filling descriptor for a frame, skb
pointer is left in the entry. Later, on the ring entry reuse, the
same entry could be used as a part of a multi-descriptor frame,
and skb for that new frame could be stored in a different entry.

Then, the stale pointer will reach the completion routine, and passed
to the release operation.

Fix that by clearing the saved skb pointer at the error path.

Fixes: d2c96b9 ("net: rswitch: Add jumbo frames handling for TX")
Signed-off-by: Nikita Yushchenko <[email protected]>
Reviewed-by: Yoshihiro Shimoda <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: nikita-yoush

drivers/net/ethernet/renesas/rswitch.c

@@ -1631,6 +1631,7 @@ static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *nd
 	return ret;
 
 err_unmap:
+	gq->skbs[(gq->cur + nr_desc - 1) % gq->ring_size] = NULL;
 	dma_unmap_single(ndev->dev.parent, dma_addr_orig, skb->len, DMA_TO_DEVICE);
 
 err_kfree: