CVE-2026-31463 Overview
A vulnerability has been identified in the Linux kernel's iomap subsystem that can lead to invalid folio access when i_blkbits differs from the I/O granularity. This issue occurs in the iomap_read_folio_iter() function where the ctx->cur_folio pointer is not properly invalidated when I/O is submitted for less than the full folio size in the !ifs (inline file system) case.
The flaw stems from an incomplete fix in commit aa35dd5cbc06 ("iomap: fix invalid folio access after folio_end_read()"), which addressed invalid folio access for folios without an ifs attached but did not handle the edge case where 1 << inode->i_blkbits matches the folio size but differs from the granularity used for I/O operations.
Critical Impact
Invalid memory access in the Linux kernel's I/O mapping subsystem could lead to system instability, kernel panics, or potential denial of service conditions on affected systems.
Affected Products
- Linux kernel (versions with vulnerable iomap implementation)
Discovery Timeline
- April 22, 2026 - CVE-2026-31463 published to NVD
- April 23, 2026 - Last updated in NVD database
Technical Details for CVE-2026-31463
Vulnerability Analysis
This vulnerability is classified as an invalid memory access issue within the Linux kernel's iomap subsystem. The root problem occurs during folio read operations when there is a mismatch between the inode's block size bits (i_blkbits) and the actual I/O granularity being used.
When 1 << inode->i_blkbits matches the folio size but differs from the I/O granularity, the system can submit I/O for less than the full folio. In this scenario, the condition if (*bytes_submitted == folio_len) in iomap_read_folio_iter() evaluates to false, meaning ctx->cur_folio is not set to NULL. Subsequently, iomap_read_end() is called on a folio that the I/O helper already owns and is actively processing, creating a race condition and invalid memory access.
Root Cause
The vulnerability originates from an incomplete patch in commit aa35dd5cbc06. While that commit addressed invalid folio access for folios without an ifs attached, it failed to account for the specific case where the inode's block size matches the folio size but the actual I/O granularity differs. This causes the ctx->cur_folio pointer to remain valid when it should be invalidated, leading to double handling of the folio between the iomap read path and the I/O completion handler.
Attack Vector
The attack vector for this vulnerability is currently unknown. As a kernel memory access issue, exploitation would typically require local access to the system and the ability to trigger specific I/O patterns that cause the mismatch between block size and I/O granularity. The vulnerability could potentially be triggered during normal filesystem operations under specific conditions, leading to system instability or denial of service.
The vulnerability manifests in the iomap_read_folio_iter() function where the conditional check for full folio submission does not account for the !ifs case with differing I/O granularity. The fix involves unconditionally invalidating ctx->cur_folio for the !ifs case to prevent the double access scenario. Technical details can be found in the Linux Kernel Commit Updates.
Detection Methods for CVE-2026-31463
Indicators of Compromise
- Kernel panic messages referencing iomap or folio operations in system logs
- Unexpected system crashes or reboots during intensive I/O operations
- Kernel oops messages containing references to iomap_read_folio_iter or iomap_read_end functions
Detection Strategies
- Monitor kernel logs (dmesg, /var/log/kern.log) for iomap-related errors or warnings
- Implement kernel crash dump analysis to identify patterns related to folio access violations
- Use kernel tracing tools (ftrace, perf) to monitor iomap subsystem behavior for anomalies
Monitoring Recommendations
- Enable kernel crash dump collection (kdump) to capture debugging information when kernel panics occur
- Set up alerting for kernel error messages containing "iomap", "folio", or "invalid page" references
- Monitor system stability metrics and correlate unexpected crashes with filesystem I/O activity patterns
How to Mitigate CVE-2026-31463
Immediate Actions Required
- Review running kernel version to determine if it contains the vulnerable iomap code
- Apply available kernel patches that address this vulnerability
- Consider updating to a patched kernel version as soon as patches become available
- Monitor system stability and investigate any kernel panics related to I/O operations
Patch Information
The Linux kernel developers have released patches to address this vulnerability. The fix involves unconditionally invalidating ctx->cur_folio for the !ifs case in the iomap_read_folio_iter() function. Patches are available through the following commits:
System administrators should update to kernel versions that include these patches through their distribution's package management system.
Workarounds
- No specific workarounds are available for this vulnerability; patching is the recommended remediation
- Ensure system monitoring is in place to detect any kernel stability issues related to I/O operations
- Maintain regular kernel security updates through distribution package management
# Check current kernel version
uname -r
# Check for available kernel updates (Debian/Ubuntu)
apt update && apt list --upgradable | grep linux
# Check for available kernel updates (RHEL/CentOS)
yum check-update kernel
# Apply kernel updates (follow your distribution's update process)
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
