CVE-2026-80561 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
libceph: fix multiple unsafe decodes in decode_locker()
decode_locker() in cls_lock_client.c contains three unsafe decode operations that allow a malicious or compromised OSD to trigger slab-out-of-bounds reads:
1. ceph_decode_copy() at the locker_id_t name field has no preceding bounds check. With p == end after ceph_start_decoding() accepts struct_len=0, this reads sizeof(ceph_entity_name) = 9 bytes past the validated buffer boundary.
2. *p += sizeof(struct ceph_timespec) after the locker_info_t header is an unchecked pointer advance. A malicious OSD can position p past end, causing all subsequent _safe checks to pass against a bogus boundary.
3. len = ceph_decode_32(p) has no preceding bounds check, and the immediately following *p += len is uncapped. A malicious OSD can send len=0xffffffff, advancing p gigabytes past end and escaping the decode window entirely.
Fix all three by replacing bare operations with their safe variants: ceph_decode_copy -> ceph_decode_copy_safe *p += sizeof(...) -> ceph_decode_skip_n ceph_decode_32(p) -> ceph_decode_32_safe *p += len -> ceph_decode_skip_n
A new label is added to return -EINVAL on any bounds violation. -EINVAL is appropriate here: the data received from the OSD is structurally malformed, which is an invalid argument to the decode contract regardless of whether the caller or the wire is at fault.
Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment can trigger this against any kernel client that issues the lock.get_info class method (e.g. during RBD exclusive lock acquisition) without any further privileges beyond OSD session establishment.
[ idryomov: use ceph_decode_skip_string() to skip description, trim
changelog ]
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Analysis
by VulDB Data Team • 08/26/2026
The Linux kernel vulnerability identified in the libceph subsystem involves critical memory safety failures within the decode_locker function located in cls_lock_client.c. This flaw allows a malicious or compromised Object Storage Daemon (OSD) to trigger slab-out-of-bounds reads by exploiting insufficient input validation during the parsing of lock information structures. The issue arises from three distinct unsafe decoding operations that fail to verify buffer boundaries before accessing memory, creating opportunities for an attacker with access to OSD session establishment to compromise kernel integrity and potentially achieve arbitrary code execution or denial of service conditions against any client interacting with Ceph storage services.
The first vulnerability point involves the ceph_decode_copy operation used on the locker_id_t name field. This function lacks a preceding bounds check, meaning it does not verify that sufficient data exists within the buffer before attempting to copy it. If an attacker crafts a packet where struct_len is zero or insufficiently sized during ceph_start_decoding, the pointer p will equal end immediately after initialization. Consequently, the subsequent decode operation attempts to read sizeof(ceph_entity_name), which equals nine bytes past the validated buffer boundary. This results in reading uninitialized kernel memory, potentially leaking sensitive information such as stack canaries, cryptographic keys, or other process data residing adjacent to the allocated slab object.
The second vulnerability stems from an unchecked pointer advancement following the locker_info_t header processing. The code performs a direct addition of sizeof(struct ceph_timespec) to the pointer p without verifying that this operation remains within the valid buffer limits. A malicious OSD can manipulate the input stream to position the pointer past the end boundary. Once the pointer exceeds the allocated region, all subsequent safety checks in the decoding logic may pass against a bogus or non-existent boundary condition. This effectively disables the protective mechanisms designed to prevent out-of-bounds access, allowing further malformed data processing that could lead to additional memory corruption or information disclosure depending on how the corrupted state is utilized by downstream kernel functions.
The third and most severe flaw involves an uncapped length field read via ceph_decode_32 followed by a direct pointer increment using *p += len. There are no bounds checks before reading this thirty-two-bit integer, nor any cap applied to its value prior to advancing the pointer. An attacker can send a maximum unsigned integer value of 0xffffffff for the length parameter. This causes the pointer p to advance gigabytes beyond the end of the buffer, completely escaping the decode window and entering arbitrary kernel memory space. Such extreme out-of-bounds access poses a critical risk as it allows reading or potentially writing to unrelated kernel structures, which can lead to full system compromise if combined with other exploitation techniques targeting specific data structures in the vicinity of the corrupted pointer state.
The operational impact of these vulnerabilities is significant within multi-tenant Ceph deployments where trust boundaries between clients and storage daemons are critical. An attacker who has established an OSD session, even without elevated privileges beyond that initial connection, can target any kernel client issuing lock.get_info class methods. This includes common operations such as RBD exclusive lock acquisition, which is frequently used in virtualized environments to ensure data consistency across multiple instances accessing the same block device. By triggering these slab-out-of-bounds reads, an attacker can destabilize the host system, cause kernel panics leading to denial of service for all tenants sharing that node, or extract sensitive information from other processes running on the compromised server through memory leakage.
The remediation strategy involves replacing the unsafe raw operations with their validated counterparts provided by the Ceph library's safe decoding API. Specifically, ceph_decode_copy is replaced with ceph_decode_copy_safe to ensure bounds are checked before copying data. The unchecked pointer arithmetic for skipping time structures is changed to use ceph_decode_skip_n, which validates that the skip operation does not exceed buffer limits. Similarly, ceph_decode_32 is swapped for ceph_decode_32_safe to prevent reading arbitrary values without validation, and the subsequent uncapped increment *p += len is replaced with ceph_decode_skip_n to ensure safe traversal of variable-length fields. These changes enforce strict adherence to buffer boundaries throughout the decoding process, eliminating the possibility of out-of-bounds access regardless of malformed input from the OSD.
Additionally, a new error handling label has been introduced to return -EINVAL whenever any bounds violation is detected during the decode operation. This approach treats structurally malformed data received from an OSD as an invalid argument to the decode contract, acknowledging that such inputs are fundamentally incorrect whether they originate from network corruption or malicious intent. By consistently returning this specific error code on validation failures, the kernel ensures that corrupted states do not propagate further into the system logic. This aligns with industry best practices for defensive programming in network-facing components, emphasizing fail-safe defaults and explicit rejection of malformed packets to maintain system stability and security integrity.
From a threat modeling perspective, this vulnerability maps directly to CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write if the pointer manipulation were extended beyond reading capabilities in future code paths or combined with other flaws. The exploitation technique aligns with ATT&CK techniques related to initial access via compromised services and potential lateral movement through memory corruption leading to privilege escalation. Security teams should prioritize patching this issue on all Ceph clients, particularly those involved in high-frequency locking operations like RBD usage. Monitoring for anomalous OSD behavior or unexpected kernel errors related to libceph decoding can serve as an indicator of attempted exploitation while patches are being deployed across the infrastructure.