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

ipv4: fib: Dont 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

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

Lets fix the inconsistent behaviour.

References

• https://git.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763
• https://git.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3d
• https://git.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31
• https://git.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8
• https://git.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443
• https://git.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305f
• https://git.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1
• https://git.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8