Re: [PATCH net] tun: free page on short-frame rejection in tun_xdp_one()

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Weiming Shi wrote:
> tun_xdp_one() returns -EINVAL on a frame shorter than ETH_HLEN without
> freeing the page that vhost_net_build_xdp() allocated for it.
> tun_sendmsg() discards that -EINVAL and still returns total_len, so
> vhost_tx_batch() takes the success path and never frees the page; each
> short frame in a batch leaks one page-frag chunk.
> 
> A local process that can open /dev/net/tun and /dev/vhost-net can hit
> this path: it attaches a tun/tap device as the vhost-net backend and
> feeds TX descriptors whose length minus the virtio-net header is below
> ETH_HLEN. Each kick leaks the page-frag chunks for that batch, and a
> tight submission loop exhausts host memory and triggers an OOM panic.
> Free the page before returning -EINVAL, matching the XDP-program error
> path in the same function.
> 
> Fixes: 049584807f1d ("tun: add missing verification for short frame")
> Reported-by: Xiang Mei <xmei5@asu.edu>
> Assisted-by: Claude:claude-opus-4-7
> Signed-off-by: Weiming Shi <bestswngs@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>