AZL-99416

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

net/packet: defer vmalloc TX_RING free until skbs finish

AFPACKET TXRING skbs keep a raw pointer to their ring frame. The skb page references preserve page-backed ring blocks after pg_vec is freed, but they do not preserve a vmalloc mapping.

tpacketdestructskb() currently drops the pending reference before writing the timestamp and TPSTATUSAVAILABLE to the frame. Move the decrement after those stores. The smp_wmb() in __packetsetstatus() orders the frame stores before the decrement.

Also recheck pending TX frames under pgveclock before non-closing ring replacement, so a racing send cannot add a pending skb between the initial check and the ring swap.

Ring allocation can produce a mixture of page-backed and vmalloc-backed blocks. Allocate deferred-work storage during TX ring setup when the first vmalloc-backed block is encountered, and keep its pointer in the pgvec allocation header. If allocation fails, return -ENOMEM from ring setup. On socket close, a non-NULL pointer identifies a vmalloc-backed vector without a scan. If TX skbs remain, defer the whole vector to systemlong_wq.

After pgvec is detached, a late destructor can skip the pending decrement. Use socket write-memory accounting as the deferred lifetime gate instead: an skb remains charged through its final sockwfree(), after all ring-frame accesses. The delayed work retains a socket reference and reschedules itself until no TX skbs remain.

Move pendingrefcnt release to packetsockdestruct() so late skb destructors and deferred cleanup can safely use it after packetrelease(). Page-backed teardown remains synchronous, and no lock is added to the TX completion hot path.