Affected: Linux

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

packet: use ubuf_info completion for TX_RING packets

tpacket_snd sends skbs with frags pointing into its ring slots. Slots are released when skb->destructor is called.

A call to skb_orphan calls skb->destructor before the skb is freed. This can cause the slot to be reused while still linked into the skb.

Switch to standard zerocopy completion (ubuf_info) so the slot is only released once all references to the payload are freed or copied. Restore skb->destructor to standard sock_wfree.

The ubuf_info completion callback can be called with a NULL skb, but only from net_zcopy_put and related API, used by zerocopy implementations that hold their own reference on the uarg, such as MSG_ZEROCOPY. This uarg is only ever completed from skb_zcopy_clear, so skb is always set.

To prevent userspace from aliasing in-flight state on shared ring slots, allocate tpacket_uarg per packet, rather than per slot. This adds a small allocation to the transmit path. Use standard kmalloc to allow backporting to stable kernels.

The uarg holds an sk_wmem_alloc reference, rather than an sk_refcnt reference. packet_free_tx_ring waits on sk_wmem_alloc before freeing the ring pages. Always allocate vec->deferred for tx_ring so page-backed rings also wait on sk_wmem_alloc when skb_copy_ubufs drops page refs before calling tpacket_ubuf_complete.

Drop the tx_ring.pg_vec test that tpacket_destruct_skb performed before accessing the slot…