CVE-2026-98885 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
ima: return error early if file xattr cannot be changed
During early boot, the filesystem is read-only and any changes to xattrs are not allowed. This fails in case of ext4 because changing xattr starts an ext4 transaction which fails with the following warning.
WARNING: fs/ext4/ext4_jbd2.c:75 at ext4_journal_check_start+0x63/0xa0 [ext4], CPU#1: systemd-sysroot/561
CPU: 1 UID: 0 PID: 561 Comm: systemd-sysroot Not tainted 6.19.12-1-default #1 PREEMPT(voluntary) openSUSE Tumbleweed c2dfc3c9d9f6f1233251c5d4410574fe82a348ee Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 RIP: 0010:ext4_journal_check_start+0x63/0xa0 [ext4]
Call Trace: __ext4_journal_start_sb+0x3e/0x180 [ext4 6d025f3bc52c89a957b89a89d211fadf5e9434e1]
ext4_xattr_set+0x104/0x150 [ext4 6d025f3bc52c89a957b89a89d211fadf5e9434e1]
__vfs_setxattr+0x9a/0xd0 __vfs_setxattr_noperm+0x76/0x1f0 ima_appraise_measurement+0x23e/0xe40 ima_d_path+0x5a/0xd0 process_measurement+0xb29/0xc40 ? copy_from_kernel_nofault+0x21/0xe0 ? fscrypt_file_open+0xc0/0xe0 ? ext4_file_open+0x60/0x490 [ext4 6d025f3bc52c89a957b89a89d211fadf5e9434e1]
? bpf_prog_31efb7c56239148b_restrict_filesystems+0xab/0x126 ? __bpf_prog_exit+0x23/0xd0 ? __bpf_tramp_exit+0xd/0x50 ? bpf_trampoline_6442530367+0x9f/0xea ima_file_check+0x57/0x80 security_file_post_open+0x50/0xf0 path_openat+0x493/0x1650 do_filp_open+0xc7/0x170
Detect the state of the file early and return the error.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel Integrity Measurement Architecture, commonly known as IMA, is a critical security subsystem responsible for measuring and attesting to the integrity of files executed or accessed by applications. A specific vulnerability was identified within this module regarding its handling of extended attributes during the early boot phase of system initialization. During this initial stage, the root filesystem is mounted in read-only mode to ensure that only verified and trusted components are loaded into memory before transitioning to a writable state. The flaw arises when IMA attempts to modify file extended attributes as part of its appraisal process while the filesystem remains locked for writing operations.
The technical core of this issue lies in the interaction between the IMA subsystem and the ext4 filesystem driver. When IMA determines that an xattr needs to be changed, it invokes standard virtual file system functions which ultimately trigger a transaction start within the ext4 journaling layer. Because the filesystem is read-only at this stage, the attempt to begin a write transaction fails immediately. This failure does not result in a clean error code being returned to the caller; instead, it triggers a kernel warning and stack trace dump via the JBD2 subsystem. The specific function involved, ext4_journal_check_start, detects that no journaling is permitted on a read-only mount and generates a loud warning message indicating an invalid operation attempt by process systemd-sysroot running under UID 0 with PID 561.
This behavior presents several operational impacts for system administrators and security engineers. First, the generation of kernel warnings during boot can clutter dmesg logs, making it difficult to identify genuine critical errors amidst routine startup noise. Second, while the operation fails safely without causing a full kernel panic in most configurations, the presence of such warnings indicates improper error handling logic within the IMA module. It suggests that the code path does not adequately check the writability status of the underlying filesystem before attempting modifications. This represents a deviation from robust defensive programming practices where state checks should precede resource-allocation or modification attempts to avoid unnecessary overhead and log pollution.
From a classification perspective, this vulnerability aligns with CWE-252, which covers unchecked return values, as the code path proceeds to execute file system operations without verifying if those operations are permissible given the current mount flags. It also relates to CWE-732, involving incorrect permission assignment, specifically regarding the assumption that write access is available when it has been explicitly restricted by the boot process configuration. In terms of MITRE ATT&CK mapping, this does not represent a direct exploit vector for privilege escalation or remote code execution but rather falls under T1562.001, Impair Defenses: Disable or Modify Tools, as improper logging and warning generation can obscure security-relevant events during the critical boot sequence where integrity checks are most vital.
The resolution involves modifying the IMA appraisal logic to detect the read-only state of the file system early in the execution flow. By checking whether the underlying superblock allows write operations before attempting any xattr modifications, the kernel can return an appropriate error code immediately rather than proceeding into the filesystem driver and triggering a journaling failure. This change ensures that integrity measurements are handled gracefully during boot without generating spurious warnings or consuming resources for doomed transactions.
To mitigate this issue in environments running affected kernels, administrators should ensure they apply the latest available patches from their distribution vendors which include this fix. For systems where immediate patching is not possible, verifying that IMA policies do not require xattr modifications on read-only mounts during early boot can reduce log noise, though this may compromise strict integrity verification for certain files until the filesystem becomes writable. Long-term mitigation involves maintaining up-to-date kernel versions to benefit from these internal logic corrections within security subsystems like IMA and LSM frameworks.