Commit d2f0c961 authored Apr 29, 2019 by Shmulik Ladkani Committed by David S. Miller May 01, 2019

ipv4: ip_do_fragment: Preserve skb_iif during fragmentation



Previously, during fragmentation after forwarding, skb->skb_iif isn't
preserved, i.e. 'ip_copy_metadata' does not copy skb_iif from given
'from' skb.

As a result, ip_do_fragment's creates fragments with zero skb_iif,
leading to inconsistent behavior.

Assume for example an eBPF program attached at tc egress (post
forwarding) that examines __sk_buff->ingress_ifindex:
 - the correct iif is observed if forwarding path does not involve
   fragmentation/refragmentation
 - a bogus iif is observed if forwarding path involves
   fragmentation/refragmentatiom

Fix, by preserving skb_iif during 'ip_copy_metadata'.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 2dcb0033

net/ipv4/ip_output.c

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -519,6 +519,7 @@ static void ip_copy_metadata(struct sk_buff to, struct sk_buff from)
	to->pkt_type = from->pkt_type;		to->pkt_type = from->pkt_type;
	to->priority = from->priority;		to->priority = from->priority;
	to->protocol = from->protocol;		to->protocol = from->protocol;
			to->skb_iif = from->skb_iif;
	skb_dst_drop(to);		skb_dst_drop(to);
	skb_dst_copy(to, from);		skb_dst_copy(to, from);
	to->dev = from->dev;		to->dev = from->dev;

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