blob: 7bccb56b61c2e32e447186aaa8cc0afb3f8f3a53 [file] [log] [blame]
From bbac07b46d9e372a4faf78fca7c7df0449acd086 Mon Sep 17 00:00:00 2001
From: Willem de Bruijn <>
Date: Mon, 27 Jan 2020 15:40:31 -0500
Subject: [PATCH] udp: segment looped gso packets correctly
commit 6cd021a58c18a1731f7e47f83e172c0c302d65e5 upstream.
Multicast and broadcast packets can be looped from egress to ingress
pre segmentation with dev_loopback_xmit. That function unconditionally
sets ip_summed to CHECKSUM_UNNECESSARY.
udp_rcv_segment segments gso packets in the udp rx path. Segmentation
usually executes on egress, and does not expect packets of this type.
__udp_gso_segment interprets !CHECKSUM_PARTIAL as CHECKSUM_NONE. But
the offsets are not correct for gso_make_checksum.
UDP GSO packets are of type CHECKSUM_PARTIAL, with their uh->check set
to the correct pseudo header checksum. Reset ip_summed to this type.
(CHECKSUM_PARTIAL is allowed on ingress, see comments in skbuff.h)
Reported-by: syzbot <>
Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
Signed-off-by: Willem de Bruijn <>
Signed-off-by: David S. Miller <>
Signed-off-by: Paul Gortmaker <>
diff --git a/include/net/udp.h b/include/net/udp.h
index 79d141d2103b..3c1ffa95e733 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -476,6 +476,9 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
if (!inet_get_convert_csum(sk))
+ if (skb->pkt_type == PACKET_LOOPBACK)
+ skb->ip_summed = CHECKSUM_PARTIAL;
/* the GSO CB lays after the UDP one, no need to save and restore any
* CB fragment