From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 10/47] net: skip virtio_net_hdr_set_proto if protocol already set
Date:   Mon, 27 Dec 2021 16:30:46 +0100
Message-Id: <20211227151321.139250343@linuxfoundation.org>
In-Reply-To: <20211227151320.801714429@linuxfoundation.org>
References: <20211227151320.801714429@linuxfoundation.org>
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From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 1ed1d592113959f00cc552c3b9f47ca2d157768f ]

virtio_net_hdr_set_proto infers skb->protocol from the virtio_net_hdr
gso_type, to avoid packets getting dropped for lack of a proto type.

Its protocol choice is a guess, especially in the case of UFO, where
the single VIRTIO_NET_HDR_GSO_UDP label covers both UFOv4 and UFOv6.

Skip this best effort if the field is already initialized. Whether
explicitly from userspace, or implicitly based on an earlier call to
dev_parse_header_protocol (which is more robust, but was introduced
after this patch).

Fixes: 9d2f67e43b73 ("net/packet: fix packet drop as of virtio gso")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20211220145027.2784293-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/virtio_net.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 22dd48c825600..a960de68ac69e 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -25,6 +25,9 @@ static inline bool virtio_net_hdr_match_proto(__be16 protocol, __u8 gso_type)
 static inline int virtio_net_hdr_set_proto(struct sk_buff *skb,
 					   const struct virtio_net_hdr *hdr)
 {
+	if (skb->protocol)
+		return 0;
+
 	switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
 	case VIRTIO_NET_HDR_GSO_TCPV4:
 	case VIRTIO_NET_HDR_GSO_UDP:
-- 
2.34.1