CVE-2023-53848

What it actually does

Race condition deadlock in md/raid5-cache r5l_exit_log() caused by incorrect ordering of conf->log=NULL assignment relative to wake_up() and flush_work() on disable_writeback_work, allowing wait_event() in r5c_disable_writeback_async() to block indefinitely while holding reconfig_mutex.

Why it matters to the business

Systems using affected Linux kernel RAID5 caching configurations may experience hangs or unresponsiveness during storage reconfiguration or module unload, leading to potential data access disruption and requiring reboots; widespread in Ubuntu cloud and server deployments but low exploitation likelihood.

How an attack unfolds

An attacker with local access triggers r5l_exit_log() via RAID device reconfiguration or shutdown while concurrent writeback disable operations are pending; the deadlock prevents completion and may lead to system unavailability, though no public exploits or threat actor campaigns are known.

How to fix it

Upgrade affected packages to the listed fixed versions: linux-azure (14.04) to 4.15.0-1023.24~14.04.1, linux-aws-hwe (16.04) to 4.15.0-1030.31~16.04.1, linux-oracle (16.04) to 4.15.0-1007.9~16.04.1, linux-azure (18.04) to 4.15.0-1023.24, linux-oracle (18.04) to 4.15.0-1007.9, linux-hwe-edge (18.04) to 5.0.0-15.16~18.04.1, linux (20.04) to 5.4.0-9.12, linux-aws (20.04) to 5.4.0-1005.5, linux-aws-5.15 (20.04) to 5.15.0-1014.18~20.04.1, linux-azure (20.04) to 5.4.0-1006.6, linux-azure-5.15 (20.04) to 5.15.0-1007.8~20.04.1, linux-azure-fde-5.15 (20.04) to 5.15.0-1019.24~20.04.1.1, linux-bluefield (20.04) to 5.4.0-1007.10, linux-gcp (20.04) to 5.4.0-1005.5.

How to confirm the fix worked

Verify kernel package versions match or exceed the fixed releases above; confirm absence of deadlock symptoms during RAID reconfiguration tests and review dmesg for related md/raid5 messages post-upgrade.

Typical attack path

1. Obtain local code execution or shell access on target system
2. Trigger RAID5 cache exit path through mdadm reconfiguration or module removal
3. Induce concurrent r5c_disable_writeback_async() call to hit wait_event() stall
4. Cause kernel hang or forced reboot

How to detect it

Review system logs for repeated wait_event stalls or reconfig_mutex contention in md/raid5-cache paths; examine dmesg and kernel logs around device reconfiguration events for signs of deadlock.

What your security team should do

• Prioritize patching all listed Ubuntu kernel packages to the exact fixed versions provided
• Monitor for kernel panics or hangs on systems with md RAID5 caching enabled
• Test RAID reconfiguration operations in staging environments after upgrade
• Apply updates within standard maintenance windows given low EPSS and no KEV listing