About vulnerability

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

ipv4: fib: Don’t ignore error route in local/main tables.

When CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added, fib_lookup() performs route lookup directly on two tables.

Since the first lookup does not properly bail out, the result of an error route in the merged local/main table could be overwritten by another route in the default table:

unshare -n

ip link set lo up

ip route add 192.168.0.0/24 dev lo table 253

ip route add unreachable 192.168.0.0/24

ip route get 192.168.0.1

192.168.0.1 dev lo table default uid 0 cache <local>

Once a random rule is added, the error route is respected:

ip rule add table 0

ip rule del table 0

ip route get 192.168.0.1

RTNETLINK answers: No route to host

Let’s fix the inconsistent behaviour.

Affected product:

AlmaLinux 9.2 ESU , Amazon Linux 2 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 7 ELS , Debian 10 ELS , Debian 11 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , TuxCare 9.6 ESU , TuxCare 9.8 ESU , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS , Ubuntu 20.04 ELS

Affected packages:

linux @ 4.19.0 (+17 more)

Live-patch status from KernelCare for each operating system.