ipv6: avoid divide by zero in rt6_multipath_rebalance

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Summary

CVECVE-2026-89790
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 09:17:09 UTC
Updated2026-09-16 09:17:09 UTC
DescriptionIn 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected bd11ff421d36abdb585b9104fa70057bf01b3110 f30cf8fd9872299c0c27f9916252ba2b9f422dce git Not specified
CNA Linux Linux affected bd11ff421d36abdb585b9104fa70057bf01b3110 f82b5dbb2fef65b52a62d5ffe05e0483c4385a83 git Not specified
CNA Linux Linux affected bd11ff421d36abdb585b9104fa70057bf01b3110 d2c26c2911dd1a363c488add4fb63eb5f0f28f87 git Not specified
CNA Linux Linux affected 6.16 Not specified
CNA Linux Linux unaffected 6.16 semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/f30cf8fd9872299c0c27f9916252ba2b9f422dce 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d2c26c2911dd1a363c488add4fb63eb5f0f28f87 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f82b5dbb2fef65b52a62d5ffe05e0483c4385a83 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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