Affected: Linux

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

vmxnet3: Fix packet corruption in vmxnet3_xdp_xmit_frame

Andrew and Nikolay reported connectivity issues with Cilium's service load-balancing in case of vmxnet3.

If a BPF program for native XDP adds an encapsulation header such as IPIP and transmits the packet out the same interface, then in case of vmxnet3 a corrupted packet is being sent and subsequently dropped on the path.

vmxnet3_xdp_xmit_frame() which is called e.g. via vmxnet3_run_xdp() through vmxnet3_xdp_xmit_back() calculates an incorrect DMA address:

page = virt_to_page(xdpf->data); tbi->dma_addr = page_pool_get_dma_addr(page) + VMXNET3_XDP_HEADROOM; dma_sync_single_for_device(&adapter->pdev->dev, tbi->dma_addr, buf_size, DMA_TO_DEVICE);

The above assumes a fixed offset (VMXNET3_XDP_HEADROOM), but the XDP BPF program could have moved xdp->data. While the passed buf_size is correct (xdpf->len), the dma_addr needs to have a dynamic offset which can be calculated as xdpf->data - (void *)xdpf, that is, xdp->data - xdp->data_hard_start.