[PATCH iwl-net v2] igc: fix potential skb leak in igc_fpe_xmit_smd_frame()

[Kohei Enju <kohei@enjuk.jp>]

When igc_fpe_init_tx_descriptor() fails, no one takes care of an
allocated skb, leaking it. [1]
Use dev_kfree_skb_any() on failure.

Tested on an I226 adapter with the following command, while injecting
faults in igc_fpe_init_tx_descriptor() to trigger the error path.
 # ethtool --set-mm $DEV verify-enabled on tx-enabled on pmac-enabled on

[1]
unreferenced object 0xffff888113c6cdc0 (size 224):
...
  backtrace (crc be3d3fda):
    kmem_cache_alloc_node_noprof+0x3b1/0x410
    __alloc_skb+0xde/0x830
    igc_fpe_xmit_smd_frame.isra.0+0xad/0x1b0
    igc_fpe_send_mpacket+0x37/0x90
    ethtool_mmsv_verify_timer+0x15e/0x300

Cc: stable@vger.kernel.org
Fixes: 5422570c0010 ("igc: add support for frame preemption verification")
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
---
Changes:
  v2:
    - change to idiomatic style with goto (Simon)
    - add Cc to stable (Alex)
    - add reprodunction steps (Alex)
  v1: https://lore.kernel.org/all/20260329145122.126040-1-kohei@enjuk.jp/
---
 drivers/net/ethernet/intel/igc/igc_tsn.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_tsn.c b/drivers/net/ethernet/intel/igc/igc_tsn.c
index 8a110145bfee..02dd9f0290a3 100644
--- a/drivers/net/ethernet/intel/igc/igc_tsn.c
+++ b/drivers/net/ethernet/intel/igc/igc_tsn.c
@@ -109,10 +109,16 @@ static int igc_fpe_xmit_smd_frame(struct igc_adapter *adapter,
 	__netif_tx_lock(nq, cpu);
 
 	err = igc_fpe_init_tx_descriptor(ring, skb, type);
-	igc_flush_tx_descriptors(ring);
+	if (err)
+		goto err_free_skb_any;
 
+	igc_flush_tx_descriptors(ring);
 	__netif_tx_unlock(nq);
+	return 0;
 
+err_free_skb_any:
+	__netif_tx_unlock(nq);
+	dev_kfree_skb_any(skb);
 	return err;
 }
 
-- 
2.51.0