UBUNTU-CVE-2026-31420

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UBUNTU-CVE-2026-31420

Summary:

Details: In the Linux kernel, the following vulnerability has been resolved: bridge: mrp: reject zero test interval to avoid OOM panic br_mrp_start_test() and br_mrp_start_in_test() accept the user-supplied interval value from netlink without validation. When interval is 0, usecs_to_jiffies(0) yields 0, causing the delayed work (br_mrp_test_work_expired / br_mrp_in_test_work_expired) to reschedule itself with zero delay. This creates a tight loop on system_percpu_wq that allocates and transmits MRP test frames at maximum rate, exhausting all system memory and causing a kernel panic via OOM deadlock. The same zero-interval issue applies to br_mrp_start_in_test_parse() for interconnect test frames. Use NLA_POLICY_MIN(NLA_U32, 1) in the nla_policy tables for both IFLA_BRIDGE_MRP_START_TEST_INTERVAL and IFLA_BRIDGE_MRP_START_IN_TEST_INTERVAL, so zero is rejected at the netlink attribute parsing layer before the value ever reaches the workqueue scheduling code. This is consistent with how other bridge subsystems (br_fdb, br_mst) enforce range constraints on netlink attributes.

References: https://ubuntu.com/security/CVE-2026-31420, https://www.cve.org/CVERecord?id=CVE-2026-31420, https://git.kernel.org/linus/fa6e24963342de4370e3a3c9af41e38277b74cf3, https://ubuntu.com/security/notices/USN-8729-1, https://ubuntu.com/security/notices/USN-8761-1, https://ubuntu.com/security/notices/USN-8729-2, https://ubuntu.com/security/notices/USN-8761-2, https://ubuntu.com/security/notices/USN-8781-1, https://ubuntu.com/security/notices/USN-8729-3, https://ubuntu.com/security/notices/USN-8793-1, https://ubuntu.com/security/notices/USN-8761-3, https://ubuntu.com/security/notices/USN-8802-1, https://ubuntu.com/security/notices/USN-8729-4, https://ubuntu.com/security/notices/USN-8793-2, https://ubuntu.com/security/notices/USN-8729-5