From: Andrea Mayer andrea.mayer@uniroma2.it
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 andrea.mayer@uniroma2.it Reviewed-by: David Ahern dsahern@kernel.org Link: https://lore.kernel.org/r/20211208195409.12169-1-andrea.mayer@uniroma2.it Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/seg6_iptunnel.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -143,6 +143,14 @@ int seg6_do_srh_encap(struct sk_buff *sk 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;