[PATCH AUTOSEL 5.7 084/274] tun: correct header offsets in napi frags mode

Sasha Levin
2020-06-09T01:02:17Z

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: Sasha Levin <sashal@kernel.org>
---
drivers/net/tun.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 44889eba1dbc..b984733c6c31 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1871,8 +1871,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
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;
}

@@ -1929,9 +1932,12 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
}

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

if (unlikely(headlen > skb_headlen(skb))) {
this_cpu_inc(tun->pcpu_stats->rx_dropped);
--
2.25.1