Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
seg6: fix the iif in the IPv6 socket control block
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.
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 6 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 6 ELS , CloudLinux 7 ELS , Oracle Linux 6 ELS
- Affected packages:
- kernel @ 4.18.0 (+9 more)
In the Linux kernel, the following vulnerability has been resolved:
seg6: fix the iif in the IPv6 socket control block
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.