[PATCH 5.13 155/156] udp: properly flush normal packet at GRO time

[Greg Kroah-Hartman]

From: Paolo Abeni <pabeni@xxxxxxxxxx>

commit b43c8909be52f2baca8884f967b418a88424494a upstream.

If an UDP packet enters the GRO engine but is not eligible
for aggregation and is not targeting an UDP tunnel,
udp_gro_receive() will not set the flush bit, and packet
could delayed till the next napi flush.

Fix the issue ensuring non GROed packets traverse
skb_gro_flush_final().

Reported-and-tested-by: Matthias Treydte <mt@xxxxxxxxxxxx>
Fixes: 18f25dc39990 ("udp: skip L4 aggregation for UDP tunnel packets")
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/udp_offload.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -525,8 +525,10 @@ struct sk_buff *udp_gro_receive(struct l
 
 		if ((!sk && (skb->dev->features & NETIF_F_GRO_UDP_FWD)) ||
 		    (sk && udp_sk(sk)->gro_enabled) || NAPI_GRO_CB(skb)->is_flist)
-			pp = call_gro_receive(udp_gro_receive_segment, head, skb);
-		return pp;
+			return call_gro_receive(udp_gro_receive_segment, head, skb);
+
+		/* no GRO, be sure flush the current packet */
+		goto out;
 	}
 
 	if (NAPI_GRO_CB(skb)->encap_mark ||