CVE-2026-80876 ring-buffer: Fix event length with forced 8-byte alignment
A flaw in the Linux kernel ring buffer causes incorrect length reporting for small events on specific architectures, potentially leading to information disclosure.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-80876?
CVE-2026-80876 is a vulnerability in Linux, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ring-buffer: Fix event length with forced 8-byte alignment
When RB_FORCE_8BYTE_ALIGNMENT is true, rb_calculate_event_length() reserves the space of event->array[0] for placing the data length and rb_update_event() stores the data length in event->array[0] accordingly. As a result the whole event length will add extra 4 bytes for sizeof(event.array[0]) unconditionally.
But ring_buffer_event_length() only subtracts the sizeof(event->array[0]) for events larger than RB_MAX_SMALL_DATA + sizeof(event->array[0]). As a result, small events on architectures with RB_FORCE_8BYTE_ALIGNMENT=true report a data length that is 4 bytes larger than expected.
To fix it, add the RB_FORCE_8BYTE_ALIGNMENT as a condition to subtract the size of that length field whenever RB_FORCE_8BYTE_ALIGNMENT is true.
This issue is observed in a riscv64 kernel with CONFIG_HAVE_64BIT_ALIGNED_ACCESS set to y, when we run ftrace selftest trace_marker_raw.tc, we get the weird log: for cases where the id is 1..100, the number of data field is 8*N, but once id exceeds 100, the number of data field becomes 8*N+4: # 1 buf: 58 00 00 00 80 5e d1 63 (number of data field is 8*1) ... # a buf: 58 ... (number of data field is 8*2) ... # 64 buf: 58 ... (number of data field is 8*13) # 65 buf: 58 ... (number of data field is 8*13+4)
After applying this change, the number of data field keeps being 8*N+4 consistently.
Which versions are affected by CVE-2026-80876?
How do I fix CVE-2026-80876?
Apply the vendor's patch.
Is CVE-2026-80876 being exploited?
There is no known exploitation of CVE-2026-80876 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-80876, DEBIAN-CVE-2026-80876, GHSA-f6hv-xhx3-9x64, UBUNTU-CVE-2026-80876.