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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Matthias Treydte <mt@waldheinz.de>
Subject: [PATCH 5.13 155/156] udp: properly flush normal packet at GRO time
Date:   Thu, 22 Jul 2021 18:32:10 +0200
Message-Id: <20210722155633.366057376@linuxfoundation.org>
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From: Paolo Abeni <pabeni@redhat.com>

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@waldheinz.de>
Fixes: 18f25dc39990 ("udp: skip L4 aggregation for UDP tunnel packets")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 ||