[PATCH net] ice: fix double-free of tx_buf skb

[Michal Schmidt <mschmidt@redhat.com>]

If ice_tso() or ice_tx_csum() fail, the error path in
ice_xmit_frame_ring() frees the skb, but the 'first' tx_buf still points
to it and is marked as valid (ICE_TX_BUF_SKB).
'next_to_use' remains unchanged, so the potential problem will
likely fix itself when the next packet is transmitted and the tx_buf
gets overwritten. But if there is no next packet and the interface is
brought down instead, ice_clean_tx_ring() -> ice_unmap_and_free_tx_buf()
will find the tx_buf and free the skb for the second time.

The fix is to reset the tx_buf type to ICE_TX_BUF_EMPTY in the error
path, so that ice_unmap_and_free_tx_buf().
Move the initialization of 'first' up, to ensure it's already valid in
case we hit the linearization error path.

The bug was spotted by AI while I had it looking for something else.
It also proposed an initial version of the patch.

I reproduced the bug and tested the fix by adding code to inject
failures, on a build with KASAN.

I looked for similar bugs in related Intel drivers and did not find any.

Fixes: d76a60ba7afb ("ice: Add support for VLANs and offloads")
Assisted-by: Claude:claude-4.6-opus-high Cursor
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
---
 drivers/net/ethernet/intel/ice/ice_txrx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.c b/drivers/net/ethernet/intel/ice/ice_txrx.c
index a5bbce68f76c..4dc535a3f34b 100644
--- a/drivers/net/ethernet/intel/ice/ice_txrx.c
+++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
@@ -2156,6 +2156,9 @@ ice_xmit_frame_ring(struct sk_buff *skb, struct ice_tx_ring *tx_ring)
 
 	ice_trace(xmit_frame_ring, tx_ring, skb);
 
+	/* record the location of the first descriptor for this packet */
+	first = &tx_ring->tx_buf[tx_ring->next_to_use];
+
 	count = ice_xmit_desc_count(skb);
 	if (ice_chk_linearize(skb, count)) {
 		if (__skb_linearize(skb))
@@ -2181,8 +2184,6 @@ ice_xmit_frame_ring(struct sk_buff *skb, struct ice_tx_ring *tx_ring)
 
 	offload.tx_ring = tx_ring;
 
-	/* record the location of the first descriptor for this packet */
-	first = &tx_ring->tx_buf[tx_ring->next_to_use];
 	first->skb = skb;
 	first->type = ICE_TX_BUF_SKB;
 	first->bytecount = max_t(unsigned int, skb->len, ETH_ZLEN);
@@ -2247,6 +2248,7 @@ ice_xmit_frame_ring(struct sk_buff *skb, struct ice_tx_ring *tx_ring)
 out_drop:
 	ice_trace(xmit_frame_ring_drop, tx_ring, skb);
 	dev_kfree_skb_any(skb);
+	first->type = ICE_TX_BUF_EMPTY;
 	return NETDEV_TX_OK;
 }
 
-- 
2.53.0