CVE-2026-46278: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-46278 Overview

CVE-2026-46278 is a null pointer dereference vulnerability in the Linux kernel's drm/imagination (powervr) GPU driver. The flaw occurs in the pvr_fw_trace_mask_set function when a user writes to the firmware trace mask debugfs entry. The driver passes incorrect data to the debugfs entry, triggering a kernel oops when the trace mask is updated. The issue was reproduced on arm64 hardware (BeagleBoard.org BeaglePlay) running a development kernel. A local user with access to the affected debugfs file can trigger a kernel crash, resulting in a denial of service.

Critical Impact

Local attackers with debugfs write access can trigger a kernel null pointer dereference, causing a system crash and denial of service.

Affected Products

• Linux kernel containing the drm/imagination (powervr) GPU driver
• Systems exposing the powervr firmware trace mask debugfs interface
• arm64 platforms using PowerVR GPUs (reproduced on BeagleBoard.org BeaglePlay)

Discovery Timeline

• 2026-06-08 - CVE-2026-46278 published to NVD
• 2026-06-08 - Last updated in NVD database

Technical Details for CVE-2026-46278

Vulnerability Analysis

The vulnerability is a kernel null pointer dereference [CWE-476] in the PowerVR GPU driver's firmware trace subsystem. When userspace writes to the firmware trace mask debugfs file, the kernel invokes pvr_fw_trace_mask_set to update the trace mask. The function receives an incorrect data pointer from the debugfs callback chain, leading to a dereference of address 0x0000000000000000.

The stack trace shows the fault originates in pvr_fw_trace_mask_set+0x78/0x154 and propagates through simple_attr_write_xsigned, debugfs_attr_write, full_proxy_write, and vfs_write. The kernel reports Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 with a level 0 translation fault, terminating the writing process and producing a kernel oops.

Root Cause

The root cause is the registration of the debugfs entry with an incorrect data pointer for the trace mask attribute. When simple_attr_write invokes the set callback, pvr_fw_trace_mask_set interprets the supplied pointer as a valid driver structure, but the underlying field is null. The fix passes the correct private data so that subsequent dereferences inside the set handler operate on valid memory.

Attack Vector

Exploitation requires local access to the system and write permission on the powervr firmware trace mask debugfs file. By default, debugfs entries are owned by root, so the practical attack surface is limited to privileged users or processes with CAP_SYS_ADMIN. Writing any value to the affected debugfs entry triggers the crash. The vulnerability does not provide code execution or privilege escalation; the impact is limited to denial of service through a kernel oops.

The vulnerability mechanism is described in prose because no proof-of-concept code is available. See the Linux Kernel Commit Update and the follow-up commit for the exact source-level fix.

Detection Methods for CVE-2026-46278

Indicators of Compromise

• Kernel log entries containing Unable to handle kernel NULL pointer dereference referencing the powervr module
• Stack traces with pvr_fw_trace_mask_set in the program counter or link register
• Unexpected process termination of shells or scripts writing to /sys/kernel/debug/dri/*/pvr_fw/trace_mask
• Kernel oops messages with Internal error: Oops: 0000000096000044 on systems using PowerVR GPUs

Detection Strategies

• Monitor dmesg and /var/log/kern.log for null pointer dereference traces involving the powervr module
• Audit access to debugfs paths under /sys/kernel/debug/dri/ on systems with PowerVR GPUs
• Track kernel crash reports from kdump or pstore referencing pvr_fw_trace_mask_set

Monitoring Recommendations

• Enable persistent kernel crash logging through pstore or kdump on arm64 PowerVR platforms
• Forward kernel logs to a centralized log management system for correlation
• Alert on any write activity to powervr debugfs interfaces by non-administrative users

How to Mitigate CVE-2026-46278

Immediate Actions Required

• Apply the upstream Linux kernel patches referenced in the commits 5dfd429591f8 and ba422758981b once available in your distribution
• Restrict debugfs mount access to root only by ensuring /sys/kernel/debug is mounted with mode 0700
• Unload the powervr kernel module on systems that do not require PowerVR GPU functionality

Patch Information

The fix is provided by two upstream commits to the Linux kernel: commit 5dfd429591f8 and commit ba422758981b. The patches correct the data pointer passed to the debugfs entry so that pvr_fw_trace_mask_set operates on the intended driver structure. Apply the corresponding stable kernel release once your distribution backports the fix.

Workarounds

• Disable or unmount debugfs on production systems where kernel debugging interfaces are not required
• Remove write permissions on the powervr firmware trace mask debugfs file using chmod 0400
• Avoid loading the powervr driver on systems that do not use Imagination PowerVR GPUs

# Restrict debugfs to root and remove write access to the affected entry
mount -o remount,mode=700 /sys/kernel/debug
chmod 0400 /sys/kernel/debug/dri/*/pvr_fw/trace_mask 2>/dev/null

# Optionally blacklist the powervr module if the GPU is not required
echo "blacklist powervr" | sudo tee /etc/modprobe.d/blacklist-powervr.conf