CVE-2026-64402 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()
When the SMB sink is used as a perf AUX sink, smb_update_buffer() calls smb_sync_perf_buffer() to copy hardware trace data into the perf AUX ring buffer pages. It derives pg_idx = head >> PAGE_SHIFT from @head, which is handle->head, and indexes dst_pages[pg_idx]. The pg_idx %= nr_pages
normalization is only applied after the first loop iteration.
This leaves the initial page index underived from the buffer size, which can result in an out-of-bounds write past dst_pages[] when head exceeds
the AUX buffer size.
Normalize head modulo the AUX buffer size before deriving the page index and offset, mirroring tmc_etr_sync_perf_buffer().
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability exists within the Linux kernel's CoreSight subsystem, specifically in the ultrasoc-smb driver component that handles performance tracing operations. This issue manifests when the SMB (System Memory Buffer) sink operates as a perf AUX sink, creating a critical security flaw that could allow unauthorized memory access patterns. The problem stems from improper buffer boundary validation during hardware trace data transfer operations, potentially enabling attackers to execute out-of-bounds memory writes.
The technical flaw occurs in the smb_sync_perf_buffer() function where the driver calculates page indices without proper modulo normalization of the buffer head pointer. When perf AUX ring buffer pages are populated with hardware trace data, the code derives pg_idx = head >> PAGE_SHIFT from handle->head without first normalizing this value against the total number of pages in the AUX buffer. This calculation only applies the modulo operation nr_pages normalization after the first loop iteration, leaving the initial page index calculation vulnerable to buffer overflow conditions.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a classic out-of-bounds write condition that could be exploited by malicious actors with kernel-level privileges or through specific attack vectors. The flaw directly relates to CWE-129 Input Validation and CWE-787 Out-of-bounds Write, both of which are categorized under the Common Weakness Enumeration framework for memory safety issues. When head exceeds the AUX buffer size, the unnormalized page index calculation causes writes past the boundaries of the dst_pages[] array, potentially corrupting adjacent memory regions or enabling privilege escalation attacks.
The mitigation strategy involves implementing proper buffer size normalization before page index derivation, mirroring the established pattern used in tmc_etr_sync_perf_buffer() function within the same subsystem. This approach ensures that the head pointer value is normalized modulo the AUX buffer size prior to calculating page indices and offsets, preventing any potential out-of-bounds memory access scenarios. The fix aligns with ATT&CK technique T1068, which addresses privilege escalation through kernel vulnerabilities, by addressing the underlying memory corruption mechanism that could enable such exploitation paths.
This vulnerability demonstrates the critical importance of proper buffer boundary checking in kernel-space drivers, particularly those handling performance tracing and hardware data collection operations. The issue highlights how seemingly minor calculation order problems can result in significant security implications when dealing with memory management and ring buffer operations in real-time systems. The resolution requires careful attention to synchronization mechanisms and buffer size validation across all subsystem components that interact with perf AUX ring buffers to maintain system integrity and prevent potential exploitation scenarios.