nexthop: take nh->lock for f6i_list walks in replace check and notify

Summary

In the Linux kernel, the following vulnerability has been resolved: nexthop: take nh->lock for f6i_list walks in replace check and notify fib6_check_nh_list() and __nexthop_replace_notify() walk nh->f6i_list during an RTNL-serialized nexthop replace without holding nh->lock. IPv6 RTM_NEWROUTE/RTM_DELROUTE run without RTNL and mutate that list under nh->lock (fib6_add_rt2node_nh(), fib6_purge_rt()), so both walks race a concurrent route delete that unlinks and frees a fib6_info: BUG: KASAN: slab-use-after-free in rt6_fill_node.isra.0 (net/ipv6/route.c:5799) Read of size 4 at addr ffff888014607e64 by task exploit/143 rt6_fill_node.isra.0 (net/ipv6/route.c:5799) fib6_rt_update (net/ipv6/route.c:6412) __nexthop_replace_notify (net/ipv4/nexthop.c:2542) rtm_new_nexthop (net/ipv4/nexthop.c:2554) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) BUG: KASAN: slab-use-after-free in fib6_check_nh_list (net/ipv4/nexthop.c:1605) Read of size 8 at addr ffff888014a7d068 by task exploit/142 fib6_check_nh_list (net/ipv4/nexthop.c:1605) rtm_new_nexthop (net/ipv4/nexthop.c:2575) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) Both walks only read the entries and take no tb6_lock, so protect them with nh->lock; fib6_rt_update() uses gfp_any(), which returns GFP_ATOMIC under the lock.

Timeline

1. Aug 15, 2026, 12:28 PM UTCCVE published
2. Oct 15, 2026, 10:09 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 081efd18326e353c6fbfdeff903a83edde953f72 · fixed in 4b296d176580a85ccbc7135ebdf66c42087b23a2; From 081efd18326e353c6fbfdeff903a83edde953f72 · fixed in bb2b072c619c1f741a6234257050f72005dc63ef; From 081efd18326e353c6fbfdeff903a83edde953f72 · fixed in 072cd1f21819dedd2252e704d255de3b0cfc61a7

• Linux Linux

  6.16

• KernelLinux

  From 6.16.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.1.8

References 3