blob: 7aea5261eb01b7b638b074149626bcd156427ad8 [file] [log] [blame]
From 1eaad4a247894c9ee066afadf4183a8afecdef13 Mon Sep 17 00:00:00 2001
From: Willem de Bruijn <>
Date: Sat, 30 May 2020 15:41:31 -0400
Subject: [PATCH] tun: correct header offsets in napi frags mode
commit 96aa1b22bd6bb9fccf62f6261f390ed6f3e7967f upstream.
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 <>
Acked-by: Petar Penkov <>
Signed-off-by: David S. Miller <>
Signed-off-by: Paul Gortmaker <>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b95caa64f6f5..ed20985cb7dd 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1909,8 +1909,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
skb->dev = tun->dev;
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);
@@ -1967,9 +1970,12 @@ 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))) {