[PATCH 4.19 005/267] tun: correct header offsets in napi frags mode

Greg Kroah-Hartman
2020-06-19T14:54:10Z

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 96aa1b22bd6bb9fccf62f6261f390ed6f3e7967f ]

Tun in IFF_NAPI_FRAGS mode calls napi_gro_frags. Unlike netif_rx and
netif_gro_receive, this expects skb->data to point to the mac layer.

But skb_probe_transport_header, __skb_get_hash_symmetric, and
xdp_do_generic in tun_get_user need skb->data to point to the network
header. Flow dissection also needs skb->protocol set, so
eth_type_trans has to be called.

Ensure the link layer header lies in linear as eth_type_trans pulls
ETH_HLEN. Then take the same code paths for frags as for not frags.
Push the link layer header back just before calling napi_gro_frags.

By pulling up to ETH_HLEN from frag0 into linear, this disables the
frag0 optimization in the special case when IFF_NAPI_FRAGS is used
with zero length iov[0] (and thus empty skb->linear).

Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Petar Penkov <ppenkov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1870,8 +1870,11 @@ drop:
skb->dev = tun->dev;
break;
case IFF_TAP:
- if (!frags)
- skb->protocol = eth_type_trans(skb, tun->dev);
+ if (frags && !pskb_may_pull(skb, ETH_HLEN)) {
+ err = -ENOMEM;
+ goto drop;
+ }
+ skb->protocol = eth_type_trans(skb, tun->dev);
break;
}

@@ -1927,8 +1930,11 @@ drop:
}

if (frags) {
+ u32 headlen;
+
/* Exercise flow dissector code path. */
- u32 headlen = eth_get_headlen(skb->data, skb_headlen(skb));
+ skb_push(skb, ETH_HLEN);
+ headlen = eth_get_headlen(skb->data, skb_headlen(skb));

if (unlikely(headlen > skb_headlen(skb))) {
this_cpu_inc(tun->pcpu_stats->rx_dropped);