CVE-2025-38192 Information

Jul 05, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

net: clear the dst when changing skb protocol

A not-so-careful NAT46 BPF program can crash the kernel if it indiscriminately flips ingress packets from v4 to v6:

BUG: kernel NULL pointer dereference address: 0000000000000000 ip6_rcv_core (net/ipv6/ip6_input.c:190:20) ipv6_rcv (net/ipv6/ip6_input.c:306:8) process_backlog (net/core/dev.c:6186:4) napi_poll (net/core/dev.c:6906:9) net_rx_action (net/core/dev.c:7028:13) do_softirq (kernel/softirq.c:462:3) netif_rx (net/core/dev.c:5326:3) dev_loopback_xmit (net/core/dev.c:4015:2) ip_mc_finish_output (net/ipv4/ip_output.c:363:8) NF_HOOK (./include/linux/netfilter.h:314:9) ip_mc_output (net/ipv4/ip_output.c:400:5) dst_output (./include/net/dst.h:459:9) ip_local_out (net/ipv4/ip_output.c:130:9) ip_send_skb (net/ipv4/ip_output.c:1496:8) udp_send_skb (net/ipv4/udp.c:1040:8) udp_sendmsg (net/ipv4/udp.c:1328:10)

The output interface has a 4->6 program attached at ingress. We try to loop the multicast skb back to the sending socket. Ingress BPF runs as part of netif_rx() pushes a valid v6 hdr and changes skb->protocol to v6. We enter ip6_rcv_core which tries to use skb_dst(). But the dst is still an IPv4 one left after IPv4 mcast output.

Clear the dst in all BPF helpers which change the protocol. Try to preserve metadata dsts those may carry non-routing metadata.

Reference

https://git.kernel.org/stable/c/2a3ad42a57b43145839f2f233fb562247658a6d9 https://git.kernel.org/stable/c/ba9db6f907ac02215e30128770f85fbd7db2fcf9 https://git.kernel.org/stable/c/bfa4d86e130a09f67607482e988313430e38f6c4 https://git.kernel.org/stable/c/e9994e7b9f7bbb882d13c8191731649249150d21

CNNVD-202507-462 (Published: 2025-07-04)

Share on: