ice: fix double-free of tx_buf skb

In the Linux kernel, the following vulnerability has been resolved:

ice: fix double-free of tx_buf skb

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.