From b16d412e5f79734033df04e97d7ea2f50a8e9fe3 Mon Sep 17 00:00:00 2001 From: Andrea Mayer Date: Wed, 8 Dec 2021 20:54:09 +0100 Subject: [PATCH] seg6: fix the iif in the IPv6 socket control block commit ae68d93354e5bf5191ee673982251864ea24dd5c upstream. When an IPv4 packet is received, the ip_rcv_core(...) sets the receiving interface index into the IPv4 socket control block (v5.16-rc4, net/ipv4/ip_input.c line 510): IPCB(skb)->iif = skb->skb_iif; If that IPv4 packet is meant to be encapsulated in an outer IPv6+SRH header, the seg6_do_srh_encap(...) performs the required encapsulation. In this case, the seg6_do_srh_encap function clears the IPv6 socket control block (v5.16-rc4 net/ipv6/seg6_iptunnel.c line 163): memset(IP6CB(skb), 0, sizeof(*IP6CB(skb))); The memset(...) was introduced in commit ef489749aae5 ("ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation") a long time ago (2019-01-29). Since the IPv6 socket control block and the IPv4 socket control block share the same memory area (skb->cb), the receiving interface index info is lost (IP6CB(skb)->iif is set to zero). As a side effect, that condition triggers a NULL pointer dereference if commit 0857d6f8c759 ("ipv6: When forwarding count rx stats on the orig netdev") is applied. To fix that issue, we set the IP6CB(skb)->iif with the index of the receiving interface once again. Fixes: ef489749aae5 ("ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation") Signed-off-by: Andrea Mayer Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20211208195409.12169-1-andrea.mayer@uniroma2.it Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv6/seg6_iptunnel.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c index de4c9826c1ce..1d641e21f23f 100644 --- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -128,6 +128,14 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto) hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb)); memset(IP6CB(skb), 0, sizeof(*IP6CB(skb))); + + /* the control block has been erased, so we have to set the + * iif once again. + * We read the receiving interface index directly from the + * skb->skb_iif as it is done in the IPv4 receiving path (i.e.: + * ip_rcv_core(...)). + */ + IP6CB(skb)->iif = skb->skb_iif; } hdr->nexthdr = NEXTHDR_ROUTING; -- 2.20.1