> With IFF_NAPI_FRAGS, tun_napi_alloc_frags() gets its skb from
> napi_get_frags(). If GRO merged the previous frame with
> GRO_MERGED_FREE, that skb was recycled by napi_reuse_skb(), which does
> not reset skb->protocol set by napi_frags_skb() for the previous frame.
>
> On the IFF_TAP path, tun_get_user() calls tun_vnet_hdr_tnl_to_skb()
> before eth_type_trans(), so the virtio header checks see the protocol
> of the previous frame: the outer protocol check of UDP tunnel GSO
> packets rejects a valid frame when the two ethertypes differ, and
> GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are dissected with
> the wrong protocol.
>
> This needs GRO to hold packets across writes, for example with
> napi_defer_hard_irqs and gro_flush_timeout set on the device.
>
> Clear skb->protocol for IFF_TAP frames, as for skbs allocated by
> tun_alloc_skb(). eth_type_trans() sets it right after.
>
> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
> Reported-by: Sashiko <[email protected]>
> Closes:
> https://lore.kernel.org/netdev/[email protected]/
> Signed-off-by: Eric Dumazet <[email protected]>
Sashiko has reviewed this patch and found no issues.
--
Sashiko AI review ยท
https://sashiko.dev/#/patchset/[email protected]?part=3
