CVE-2026-53012

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> nexthop: fix IPv6 route referencing IPv4 nexthop<br /> <br /> syzbot reported a panic [1] [2].<br /> <br /> When an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag<br /> of all groups containing this nexthop is not updated. This is because<br /> nh_group_v4_update is only called when replacing AF_INET to AF_INET6,<br /> but the reverse direction (AF_INET6 to AF_INET) is missed.<br /> <br /> This allows a stale has_v4=false to bypass fib6_check_nexthop, causing<br /> IPv6 routes to be attached to groups that effectively contain only AF_INET<br /> members. Subsequent route lookups then call nexthop_fib6_nh() which<br /> returns NULL for the AF_INET member, leading to a NULL pointer<br /> dereference.<br /> <br /> Fix by calling nh_group_v4_update whenever the family changes, not just<br /> AF_INET to AF_INET6.<br /> <br /> Reproducer:<br /> # AF_INET6 blackhole<br /> ip -6 nexthop add id 1 blackhole<br /> # group with has_v4=false<br /> ip nexthop add id 100 group 1<br /> # replace with AF_INET (no -6), has_v4 stays false<br /> ip nexthop replace id 1 blackhole<br /> # pass stale has_v4 check<br /> ip -6 route add 2001:db8::/64 nhid 100<br /> # panic<br /> ping -6 2001:db8::1<br /> <br /> [1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0<br /> [2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3