Commit 6cd021a5 authored Jan 27, 2020 by Willem de Bruijn Committed by David S. Miller Jan 28, 2020

udp: segment looped gso packets correctly



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 <syzkaller@googlegroups.com>
Fixes: cf329aa4 ("udp: cope with UDP GRO packet misdirection")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 3127642d

include/net/udp.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -476,6 +476,9 @@ static inline struct sk_buff udp_rcv_segment(struct sock sk,
		if (!inet_get_convert_csum(sk))
		features \|= NETIF_F_IP_CSUM \| NETIF_F_IPV6_CSUM;

		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
		*/

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