CVE-2026-99079: net/mlx5e: Prevent stale XSK buffer release on refill retry

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

net/mlx5e: Prevent stale XSK buffer release on refill retry

When an XDP redirect to an AFXDP socket fails because its RX ring is full, the XSK core frees the buffer. During the subsequent batched refill of a legacy cyclic RQ, mlx5e also releases the WQE's XSK buffer before allocating a replacement. If that refill succeeds only partially, a WQE left without a replacement retains its old buffer pointer.

The buffer can meanwhile be allocated to another WQE. A later refill retry can then free the live buffer through the stale pointer and publish the same UMEM frame twice.

Mark the WQE as released immediately after the driver-side free. The flag is already cleared when a replacement buffer is assigned, so refill retries no longer release stale pointers.

The failure is silent and produces no kernel warning or splat. A standalone legacy cyclic-RQ zero-copy libxsk reproducer, using 64-byte UDP traffic offered at 12 Mpps, detected it: stock stopped after 2,854,914 packets in 4.094 seconds, with 4,542 xdprxringfull events and 64 ownership/double-publication errors. With this change it processed 356,904,225 packets in 30 seconds despite 571,405 xdprxringfull events, with no ownership or data errors.