CVE-2024-53047

What it actually does

Missing rcu_read_lock around mptcp_sched_find call during MPTCP socket initialization allows RCU-list traversal outside a reader section, triggering lockdep warnings under CONFIG_PROVE_RCU_LIST.

Why it matters to the business

May produce kernel warnings or subtle scheduler selection issues on systems using MPTCP; low operational disruption but requires patching to avoid debug noise and maintain kernel integrity on affected Ubuntu releases.

How an attack unfolds

An attacker would need to trigger MPTCP socket creation under specific RCU debug configurations; the flaw itself is a locking omission rather than a directly exploitable memory error, with no public weaponization observed.

How to fix it

Upgrade to fixed package versions such as linux 3.13.0-74.118, linux-aws 4.4.0-1002.2, linux 4.4.0-2.16, linux-hwe 4.8.0-36.36~16.04.1 or later equivalents for each affected Ubuntu release.

How to confirm the fix worked

Verify package versions match or exceed the listed fixed releases; confirm absence of the RCU warning when creating MPTCP sockets with CONFIG_PROVE_RCU_LIST enabled.

Typical attack path

1. Create an MPTCP socket via socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP)
2. Kernel executes mptcp_init_sock which calls mptcp_sched_find without holding rcu_read_lock
3. RCU-protected scheduler list is traversed outside reader section
4. Lockdep reports suspicious RCU usage warning

How to detect it

Search kernel logs and dmesg for strings referencing mptcp_sched_find and RCU-list traversed in non-reader section; inspect for calls originating from mptcp_init_sock.

• mptcp_sched_find
• RCU-list traversed in non-reader section
• net/mptcp/sched.c:44

What your security team should do

• Prioritize patching Ubuntu kernels on any systems using MPTCP
• Monitor for kernel log messages containing mptcp_sched_find RCU warnings
• Apply the exact fixed versions provided for each linux-* package