CVE-2025-38267 in Linux
Summary
by MITRE • 07/10/2025
In the Linux kernel, the following vulnerability has been resolved:
ring-buffer: Do not trigger WARN_ON() due to a commit_overrun
When reading a memory mapped buffer the reader page is just swapped out with the last page written in the write buffer. If the reader page is the same as the commit buffer (the buffer that is currently being written to) it was assumed that it should never have missed events. If it does, it triggers a WARN_ON_ONCE().
But there just happens to be one scenario where this can legitimately happen. That is on a commit_overrun. A commit overrun is when an interrupt preempts an event being written to the buffer and then the interrupt adds so many new events that it fills and wraps the buffer back to the commit. Any new events would then be dropped and be reported as "missed_events".
In this case, the next page to read is the commit buffer and after the swap of the reader page, the reader page will be the commit buffer, but this time there will be missed events and this triggers the following warning:
------------[ cut here ]------------
WARNING: CPU: 2 PID: 1127 at kernel/trace/ring_buffer.c:7357 ring_buffer_map_get_reader+0x49a/0x780 Modules linked in: kvm_intel kvm irqbypass CPU: 2 UID: 0 PID: 1127 Comm: trace-cmd Not tainted 6.15.0-rc7-test-00004-g478bc2824b45-dirty #564 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:ring_buffer_map_get_reader+0x49a/0x780 Code: 00 00 00 48 89 fe 48 c1 ee 03 80 3c 2e 00 0f 85 ec 01 00 00 4d 3b a6 a8 00 00 00 0f 85 8a fd ff ff 48 85 c0 0f 84 55 fe ff ff <0f> 0b e9 4e fe ff ff be 08 00 00 00 4c 89 54 24 58 48 89 54 24 50 RSP: 0018:ffff888121787dc0 EFLAGS: 00010002 RAX: 00000000000006a2 RBX: ffff888100062800 RCX: ffffffff8190cb49 RDX: ffff888126934c00 RSI: 1ffff11020200a15 RDI: ffff8881010050a8 RBP: dffffc0000000000 R08: 0000000000000000 R09: ffffed1024d26982 R10: ffff888126934c17 R11: ffff8881010050a8 R12: ffff888126934c00 R13: ffff8881010050b8 R14: ffff888101005000 R15: ffff888126930008 FS: 00007f95c8cd7540(0000) GS:ffff8882b576e000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f95c8de4dc0 CR3: 0000000128452002 CR4: 0000000000172ef0 Call Trace: <TASK> ? __pfx_ring_buffer_map_get_reader+0x10/0x10 tracing_buffers_ioctl+0x283/0x370 __x64_sys_ioctl+0x134/0x190 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x7f95c8de48db Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00 RSP: 002b:00007ffe037ba110 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007ffe037bb2b0 RCX: 00007f95c8de48db RDX: 0000000000000000 RSI: 0000000000005220 RDI: 0000000000000006 RBP: 00007ffe037ba180 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffe037bb6f8 R14: 00007f95c9065000 R15: 00005575c7492c90 </TASK> irq event stamp: 5080 hardirqs last enabled at (5079): [<ffffffff83e0adb0>] _raw_spin_unlock_irqrestore+0x50/0x70
hardirqs last disabled at (5080): [<ffffffff83e0aa83>] _raw_spin_lock_irqsave+0x63/0x70
softirqs last enabled at (4182): [<ffffffff81516122>] handle_softirqs+0x552/0x710
softirqs last disabled at (4159): [<ffffffff815163f7>] __irq_exit_rcu+0x107/0x210
---[ end trace 0000000000000000 ]---
The above was triggered by running on a kernel with both lockdep and KASAN as well as kmemleak enabled and executing the following command:
# perf record -o perf-test.dat -a -- trace-cmd record --nosplice -e all -p function hackbench 50
With perf interjecting a lot of interrupts and trace-cmd enabling all events as well as function tracing, with lockdep, KASAN and kmemleak enabled, it could cause an interrupt preempting an event being written to add enough event ---truncated---
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Analysis
by VulDB Data Team • 12/07/2025
The vulnerability described in CVE-2025-38267 resides within the Linux kernel's ring buffer implementation, specifically in how it handles memory-mapped buffer reads and commit overrun scenarios. This flaw manifests as an unintended WARN_ON_ONCE() trigger that occurs during the swapping of reader pages with committed buffer pages. The kernel's tracing subsystem utilizes ring buffers to store trace events, and when a reader page is swapped with the commit buffer—a page currently being written to—the system assumes no events should be missed. However, under specific interrupt preemption conditions, events can indeed be missed, leading to the warning. This vulnerability is particularly relevant in high-interrupt-load environments where tracing activities are intensive, such as when using perf with function tracing enabled alongside lockdep, KASAN, and kmemleak. The issue is rooted in the assumption that if a reader page becomes the commit buffer, no missed events should occur, which fails to account for legitimate commit overrun scenarios where interrupts preempt trace writing and cause buffer wrapping.
The technical mechanism behind this vulnerability involves the ring buffer's memory mapping and page swapping logic. When a reader accesses a memory-mapped trace buffer, the system swaps the reader page with the last page written to the buffer. If this swap results in the reader page becoming the commit buffer, and if there are missed events due to a commit overrun, the system triggers a warning. The commit overrun happens when an interrupt preempts an event being written and subsequently adds enough events to fill and wrap the buffer back to the commit buffer, causing new events to be dropped. The warning is generated at kernel/trace/ring_buffer.c line 7357 in the ring_buffer_map_get_reader function, indicating that the system incorrectly assumes that if the reader page is the commit buffer, there should be no missed events. This design flaw stems from a lack of proper handling for the specific case where a commit overrun legitimately causes missed events, violating the kernel's assumption about buffer consistency. The vulnerability is classified under CWE-252, which represents an "Unchecked Return Value" or improper handling of exceptional conditions, and aligns with ATT&CK technique T1059.001 for execution through system commands, particularly in contexts involving kernel tracing and debugging.
The operational impact of this vulnerability is significant in environments where high-frequency tracing and debugging are required. Systems using perf with extensive tracing capabilities, function tracing, and memory debugging features like lockdep, KASAN, and kmemleak are particularly susceptible to triggering this warning. The false positive warning can lead to unnecessary system alerts, potentially masking real issues or causing confusion during debugging sessions. While the vulnerability itself does not directly compromise system security or lead to privilege escalation, it affects system stability and trace reliability, especially in production environments where accurate tracing is critical for performance monitoring and troubleshooting. The warning can occur during normal system operation when tracing is active, particularly under interrupt-heavy workloads, leading to increased system noise and reduced confidence in trace data integrity. This issue particularly affects kernel developers and system administrators who rely on accurate tracing information for debugging, performance analysis, and system monitoring, as the warning may obscure genuine trace inconsistencies.
Mitigation strategies for this vulnerability focus on correcting the assumption within the ring buffer implementation that missed events cannot occur when a reader page becomes the commit buffer. The fix involves modifying the ring_buffer_map_get_reader function to properly account for commit overrun scenarios and avoid triggering WARN_ON_ONCE() in legitimate cases. This requires updating the kernel code to distinguish between genuine consistency errors and expected behavior during interrupt preemption. System administrators should ensure their kernels are updated to versions containing the patched implementation, as the vulnerability is resolved through kernel-level code modifications. Organizations using intensive tracing workloads with perf and function tracing should also consider temporarily disabling certain debugging features during high-load periods to reduce the likelihood of triggering the warning. Additionally, monitoring systems should be configured to distinguish between legitimate warnings and this specific false positive, as the warning can be filtered out in kernel configurations where the specific conditions for the commit overrun are not expected to occur. The fix should be validated through comprehensive testing in environments that replicate the original triggering conditions to ensure no regression in tracing functionality or system stability.