CVE-2026-89790

Summary

In the Linux kernel, the following vulnerability has been resolved:

ipv6: avoid divide by zero in rt6_multipath_rebalance

rt6_multipath_rebalance() calculates the total eligible nexthop weight in one pass and programs upper bounds in a second pass. Since RTM_NEWROUTE is RTNL-free, a concurrent ignore_routes_with_linkdown update can make the first pass return zero while the second sees an eligible nexthop, causing rt6_upper_bound_set() to divide by zero.

UBSAN: division-overflow in net/ipv6/route.c:4845:17 Oops: divide error: 0000 [#1] SMP KASAN NOPTI rt6_upper_bound_set() net/ipv6/route.c:4845 rt6_multipath_rebalance() fib6_add_rt2node() ip6_route_multipath_add() inet6_rtm_newroute()

Skip upper-bound calculation when the first pass reports a zero total. This respects the lock-free performance considerations here and solves insecure scenarios.

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxbd11ff421d36abdb585b9104fa70057bf01b3110 < f30cf8fd9872299c0c27f9916252ba2b9f422dceaffected
LinuxLinuxbd11ff421d36abdb585b9104fa70057bf01b3110 < f82b5dbb2fef65b52a62d5ffe05e0483c4385a83affected
LinuxLinuxbd11ff421d36abdb585b9104fa70057bf01b3110 < d2c26c2911dd1a363c488add4fb63eb5f0f28f87affected
LinuxLinux6.16affected
LinuxLinux0 < 6.16unaffected
LinuxLinux6.18.52 <= 6.18.*unaffected
LinuxLinux7.2.6 <= 7.2.*unaffected
LinuxLinux7.3-rc1 <= *unaffected

Weaknesses

References