CVE-2026-89503 in Linux
Summary
by MITRE • 09/12/2026
In the Linux kernel, the following vulnerability has been resolved:
ring-buffer: Fix subbuf resize race with ring_buffer_alloc_read_page()
ring_buffer_alloc_read_page() is racy with ring_buffer_subbuf_order_set, it can allocate a reader page with an outdated order. This isn't a big issue, the user can still re-allocate a new reader page and try again.
However, what is more problematic is if the value of subbuf_order changes in the middle of ring_buffer_alloc_read_page(). In that case, bpage->order might not match the actual allocated memory.
Use bpage->order for the allocation to prevent this race.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel's tracing infrastructure relies heavily on a sophisticated ring buffer mechanism designed to capture high-frequency events with minimal overhead while ensuring data integrity during concurrent access. A critical synchronization flaw was identified within the interaction between the function responsible for allocating read pages and the routine that modifies sub-buffer ordering parameters. Specifically, the race condition exists between ring_buffer_alloc_read_page() and ring_buffer_subbuf_order_set(). Under normal operation, these functions must coordinate to ensure that memory allocations align with the current configuration of the buffer's internal structure. The vulnerability arises because ring_buffer_alloc_read_page() does not strictly synchronize its allocation size with the dynamic order value maintained by the sub-buffer management logic during the critical window of page allocation.
This race condition manifests when the subbuf_order is modified concurrently while a reader process attempts to allocate a new read page. In such scenarios, the allocated memory block may be sized according to an outdated or inconsistent view of the buffer's configuration. Consequently, the order field stored in the bpage structure might not accurately reflect the actual size and layout of the allocated memory region. This discrepancy creates a state where internal pointers and offsets calculated based on the assumed page order could point to invalid memory locations or overlap with adjacent data structures. Although immediate exploitation leading to arbitrary code execution is unlikely due to the nature of kernel tracing buffers, this inconsistency poses significant risks for system stability and data integrity during high-load scenarios involving frequent trace buffer reconfiguration.
The operational impact of this vulnerability primarily centers on potential kernel panics or undefined behavior when the tracer attempts to access memory regions that do not match their expected dimensions. If a reader page is allocated with an order value that does not correspond to the actual physical memory layout, subsequent read operations may trigger page faults, corrupt trace data, or cause the tracing subsystem to crash. This can result in denial of service for applications relying on kernel tracing features such as ftrace or perf events. Furthermore, if security monitoring tools depend on accurate and continuous trace logs, this race condition could lead to gaps in observability, potentially allowing malicious activities to go undetected during periods of buffer reconfiguration.
To mitigate this vulnerability, the fix enforces strict synchronization by ensuring that ring_buffer_alloc_read_page() uses the current bpage->order value for its allocation logic rather than relying on cached or potentially stale order parameters. This adjustment guarantees that memory allocations are always consistent with the active configuration of the ring buffer sub-buffers. System administrators and developers should ensure their Linux kernels are updated to include this patch, which is typically distributed through standard kernel security updates. Additionally, minimizing frequent changes to trace buffer configurations during high-throughput tracing sessions can reduce the window of exposure for similar race conditions in other parts of the subsystem. Adhering to best practices for concurrent access control within kernel modules remains essential for maintaining robust system integrity and preventing subtle synchronization bugs from escalating into critical failures.