CVE-2023-53768

What it actually does

Out-of-bounds write during allocation of a 2D config buffer in regmap_add_irq_chip_fwnode() when num_config_regs exceeds num_config_bases, resulting in memory corruption within the kmalloc-8 cache.

Why it matters to the business

Kernel crashes and device instability on affected Linux systems, especially during boot on hardware using regmap IRQ chips; forces emergency patching and potential downtime for Ubuntu Azure workloads.

How an attack unfolds

An attacker with local code execution or the ability to influence device firmware triggers regmap_add_irq_chip_fwnode() during IRQ chip registration; the incorrect loop count causes writes beyond the allocated rows, corrupting adjacent kernel memory and leading to a crash or potential escalation.

How to fix it

Upgrade linux-azure on Ubuntu 14.04 LTS to version 4.15.0-1127.140~14.04.1 or later; apply the upstream regmap-irq fix that corrects the allocation loop termination condition.

How to confirm the fix worked

Confirm the running kernel version matches or exceeds the listed fixed package; attempt to load the affected IRQ chip configuration and verify absence of KASAN reports or crashes during regmap_add_irq_chip_fwnode().

Typical attack path

1. Obtain local execution or control device tree/firmware that loads a regmap IRQ chip
2. Trigger regmap_add_irq_chip_fwnode() with num_config_regs > num_config_bases
3. Cause the loop to perform excess allocations that write outside the pointer array
4. Corrupt kernel memory leading to KASAN-detected invalid access or system panic

How to detect it

Review kernel boot and dmesg logs for KASAN reports mentioning regmap_add_irq_chip_fwnode and invalid-access writes; inspect init process crashes on db845c or similar Qualcomm-based devices.

What your security team should do

• Prioritize patching all linux-azure 14.04 instances to 4.15.0-1127.140~14.04.1 within the next maintenance window
• Monitor kernel logs for KASAN invalid-access reports referencing regmap_add_irq_chip_fwnode
• Test device boot sequences on representative hardware after upgrade to confirm IRQ registration succeeds