On 2020/04/02 1:15, Jesper Dangaard Brouer wrote:
...
[PATCH RFC net-next] veth: adjust hard_start offset on redirect XDP frames
When native XDP redirect into a veth device, the frame arrives in the
xdp_frame structure. It is then processed in veth_xdp_rcv_one(),
which can run a new XDP bpf_prog on the packet. Doing so requires
converting xdp_frame to xdp_buff, but the tricky part is that
xdp_frame memory area is located in the top (data_hard_start) memory
area that xdp_buff will point into.
The current code tried to protect the xdp_frame area, by assigning
xdp_buff.data_hard_start past this memory. This results in 32 bytes
less headroom to expand into via BPF-helper bpf_xdp_adjust_head().
This protect step is actually not needed, because BPF-helper
bpf_xdp_adjust_head() already reserve this area, and don't allow
BPF-prog to expand into it. Thus, it is safe to point data_hard_start
directly at xdp_frame memory area.
Cc: Toshiaki Makita <makita.toshiaki@xxxxxxxxxxxxx>
FYI: This mail address is deprecated.
Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring")
Reported-by: Mao Wenan <maowenan@xxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
FWIW,
Acked-by: Toshiaki Makita <toshiaki.makita1@xxxxxxxxx>
