CVE-2026-99028: net: xilinx: axienet: Free outstanding DMA buffers on dmaengine stop

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

net: xilinx: axienet: Free outstanding DMA buffers on dmaengine stop

In the dmaengine path the driver pre-submits RX buffers and holds in-flight TX buffers whose SKBs are DMA-mapped by the driver and freed only in the completion callbacks. On ndostop() dmaengineterminatesync() aborts these descriptors without running their callbacks, and the driver then frees only the ring shells, leaking every SKB still owned by the engine and its DMA mapping on each ifdown. With 128 RX buffers pre-posted per channel, the mapping leak can eventually exhaust a limited IOMMU aperture.

Clear the slot's skb in the TX and RX callbacks so a non-NULL skb marks a slot that still owns a live, DMA-mapped buffer, and on stop unmap and free every such buffer.

axienetdmarxcb() runs from the DMA tasklet and re-arms the RX ring on each completion, so it can race axienetstop(): a completion may submit a fresh buffer after dmaengineterminatesync() has returned, leaving the channel armed with a buffer the teardown then frees while the engine may still write into it (dmareleasechannel() does not stop it either). Add a lock that axienetdmarxcb() holds across the @stopping check and the resubmit, and axienetstop() holds to set @stopping before terminating. Once @stopping is set no callback can arm a new buffer, and any armed just before is aborted by the terminate, so teardown only frees buffers the engine no longer owns.