CVE-2021-47363

/// Technical description

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

nexthop: Fix division by zero while replacing a resilient group

The resilient nexthop group torture tests in fib_nexthop.sh exposed a

possible division by zero while replacing a resilient group [1]. The

division by zero occurs when the data path sees a resilient nexthop

group with zero buckets.

The tests replace a resilient nexthop group in a loop while traffic is

forwarded through it. The tests do not specify the number of buckets

while performing the replacement, resulting in the kernel allocating a

stub resilient table (i.e, 'struct nh_res_table') with zero buckets.

This table should never be visible to the data path, but the old nexthop

group (i.e., 'oldg') might still be used by the data path when the stub

table is assigned to it.

Fix this by only assigning the stub table to the old nexthop group after

making sure the group is no longer used by the data path.

Tested with fib_nexthops.sh:

Tests passed: 222

T

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References