CVE-2024-35998

What it actually does

Potential deadlock (ORDER_REVERSAL) in cifs_sync_mid_result when spin_lock for TCP_Server_Info.srv_lock is acquired while holding TCP_Server_Info.mid_lock.

Why it matters to the business

Linux systems using SMB3/CIFS file sharing may experience hangs or crashes leading to service disruption and operational downtime, especially in environments with high kernel dependency counts.

How an attack unfolds

An attacker triggers concurrent SMB3 operations on a Linux system that cause the cifs_sync_mid_result function to acquire locks in the reverse order, resulting in a deadlock condition.

How to fix it

Upgrade Linux kernel to version 6.1.90 or later; apply commit c7a4bca289e50bb4b2650f845c41bb3e453f4c66 in stable trees.

How to confirm the fix worked

Verify running kernel version is at or above 6.1.90; confirm presence of the lock-ordering fix in cifs_sync_mid_result source.

Typical attack path

1. Establish SMB3/CIFS connection to target Linux system
2. Issue multiple concurrent file or session operations to exercise mid and server lock paths
3. Force lock acquisition order reversal in cifs_sync_mid_result to induce deadlock

How to detect it

Review kernel logs for hung-task or deadlock warnings referencing cifs mid or srv lock functions; inspect SMB3 connection traces for prolonged lock contention.

What your security team should do

• Prioritize kernel upgrade to 6.1.90 across all affected Linux deployments due to 877 days since publication
• Monitor EPSS trend and reassess if exploitation maturity increases
• Test SMB3 workloads post-upgrade to ensure no regression in file-sharing stability