CVE-2026-46258: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-46258 Overview

CVE-2026-46258 is a NULL pointer dereference vulnerability in the Linux kernel's GPIO character device (gpio: cdev) subsystem. The flaw resides in the linehandle_create() function, where a call to retain_and_null_ptr(lh) nullifies the lh pointer. A subsequent debug print statement then dereferences lh, causing a kernel crash. The upstream fix replaces the dereferenced field with the equivalent value from handlereq.lines, preserving the diagnostic output without referencing the freed pointer.

Critical Impact

Local users invoking the GPIO character device interface can trigger a kernel NULL pointer dereference, resulting in a denial of service through a kernel crash.

Affected Products

• Linux kernel versions containing the linehandle_create() implementation in drivers/gpio/gpiolib-cdev.c
• Distributions shipping kernels prior to the stable backport commits referenced in the kernel.org git tree
• Embedded and server platforms exposing the GPIO character device interface (/dev/gpiochipN)

Discovery Timeline

• 2026-06-03 - CVE-2026-46258 published to NVD
• 2026-06-03 - Last updated in NVD database

Technical Details for CVE-2026-46258

Vulnerability Analysis

The vulnerability is a NULL pointer dereference [CWE-476] in the Linux kernel GPIO character device driver. The linehandle_create() function manages the creation of line handles used to interact with GPIO lines from user space through the character device ABI.

During the creation flow, the function uses the retain_and_null_ptr() helper against the local lh pointer. This macro intentionally clears the local variable after retaining its value elsewhere, ensuring the cleanup path does not double-free the structure. After this point, lh is NULL and must not be dereferenced.

A debug print statement placed after the nulling operation still dereferences lh to read a field describing the number of GPIO lines configured. When the debug path is reached, the kernel oopses on the NULL access, terminating the calling context.

Root Cause

The root cause is improper ordering of pointer invalidation and pointer use within linehandle_create(). The diagnostic logging code was authored against a pointer that is no longer valid at that program point. The upstream patch resolves the issue by using handlereq.lines, a stack-resident value that holds the same data and remains valid through the debug print.

Attack Vector

The attack surface is local. A process must hold an open file descriptor to a GPIO character device (/dev/gpiochipN) and issue the GPIO_GET_LINEHANDLE_IOCTL ioctl. Reaching the vulnerable code path requires permissions granted to the GPIO device node, typically restricted to root or users in a privileged group on most distributions. Triggering the crash yields a local denial of service against the kernel.

The vulnerability is described in prose rather than reproduction code. Consult the upstream commits 6af6be278e3b and 87b9d7a4cfbe for the exact source diff.

Detection Methods for CVE-2026-46258

Indicators of Compromise

• Kernel oops or panic messages referencing linehandle_create in the call stack within dmesg or /var/log/kern.log
• NULL pointer dereference faults originating from gpiolib-cdev.c
• Unexpected process terminations or system instability tied to userland tools that open /dev/gpiochipN

Detection Strategies

• Compare the installed kernel version and build against the fixed commits in the stable trees on git.kernel.org
• Audit hosts for processes opening GPIO character devices and the privileges granted to them
• Monitor kernel ring buffer output for crash signatures involving GPIO ioctl paths

Monitoring Recommendations

• Forward kernel logs to a centralized logging or SIEM platform and alert on BUG: or Oops: entries referencing GPIO subsystems
• Track ioctl activity on /dev/gpiochip* devices using auditd rules
• Correlate node reboots or kernel panics on embedded and IoT fleets with GPIO workload telemetry

How to Mitigate CVE-2026-46258

Immediate Actions Required

• Apply the stable kernel update containing the linehandle_create() fix to all affected systems
• Restrict access to /dev/gpiochip* device nodes to trusted users and service accounts only
• Inventory embedded, IoT, and industrial Linux assets that expose GPIO interfaces and prioritize them for patching

Patch Information

The vulnerability is resolved upstream by replacing the post-nulled lh->... dereference with the equivalent handlereq.lines value. The fix is available in the Linux stable tree via commits 6af6be278e3b and 87b9d7a4cfbe. Rebuild or upgrade to a distribution kernel that incorporates these commits.

Workarounds

• Tighten permissions on GPIO character devices via udev rules so only required service accounts retain access
• Disable or unload GPIO character device functionality on systems that do not require user-space GPIO control
• Where kernel rebuilds are not immediately possible, isolate affected hosts from untrusted local users until patches are deployed

# Example udev rule restricting GPIO character device access
# /etc/udev/rules.d/99-gpio-restrict.rules
KERNEL=="gpiochip*", OWNER="root", GROUP="gpio", MODE="0660"