ip6mr: do not clone dst in ip6mr_cache_report()

Summary

In the Linux kernel, the following vulnerability has been resolved: ip6mr: do not clone dst in ip6mr_cache_report() IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU. When an ingress multicast packet misses MFC lookup, ip6mr_cache_unresolved() places the skb onto the unresolved queue, escaping the receive-side RCU grace period. If the underlying route is deleted and freed, and the MFC queue is later resolved with a wrong parent interface, ip6_mr_forward() invokes ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab use-after-free. Report packets queued to mroute6_sk (a raw socket) and netlink notifications do not require an attached dst entry. Fix this by: 1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs do not hold a dst. 2. Dropping skb_dst before queuing unresolved skbs in ip6mr_cache_unresolved(), matching the fact that multicast forwarding resolves outgoing routes anew via ip6_route_output().

Timeline

1. Sep 17, 2026, 4:06 PM UTCCVE published
2. Oct 21, 2026, 12:49 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 67f415dd29063a5906c560051c00e42dcf01a4dd · fixed in 7f8287f606c8c028d4224e85d95dc448c6d6d623; From 67f415dd29063a5906c560051c00e42dcf01a4dd · fixed in 42ef371466d5648f5c9e8bc219f0af0a2c2bbf8c; From 67f415dd29063a5906c560051c00e42dcf01a4dd · fixed in f57b0fd1c62e1be274ee154ab7fb8ac4481b7f89; From 67f415dd29063a5906c560051c00e42dcf01a4dd · fixed in 4a674afaae4136c71943aa3e35d433676fd40e8f; From 67f415dd29063a5906c560051c00e42dcf01a4dd · fixed in 235b42b5860189eb8c27c36435ad932cae65a734

• Linux Linux

  5.3

• KernelLinux

  From 5.3.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.6

References 5