CVE-2026-89790
Description
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.
How to fix
- Linux Linuxf30cf8fd9872299c0c27f9916252ba2b9f422dce, f82b5dbb2fef65b52a62d5ffe05e0483c4385a83, d2c26c2911dd1a363c488add4fb63eb5f0f28f87 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Linux Linux | bd11ff421d36abdb585b9104fa70057bf01b3110 ≤ v < f30cf8fd9872299c0c27f9916252ba2b9f422dce, bd11ff421d36abdb585b9104fa70057bf01b3110 ≤ v < f82b5dbb2fef65b52a62d5ffe05e0483c4385a83, bd11ff421d36abdb585b9104fa70057bf01b3110 ≤ v < d2c26c2911dd1a363c488add4fb63eb5f0f28f87, 6.16 | f30cf8fd9872299c0c27f9916252ba2b9f422dce, f82b5dbb2fef65b52a62d5ffe05e0483c4385a83, d2c26c2911dd1a363c488add4fb63eb5f0f28f87 |
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