CVE-2026-89771

In the Linux kernel, the following vulnerability has been resolved:

ring-buffer: Fix subbuf resize race with ring buffer readers

trace_buffer subbuf_size is read lockless in ring_buffer_read_page() and

ring_buffer_read_start(), while it can simultaneously be resized with

ring_buffer_subbuf_order_set().

Instead of trace_buffer::subbuf_size, use bpage::order in

ring_buffer_read_start() and ring_buffer_read_page().

In ring_buffer_read_start(), even with resize_disabled, there is still a

possibility of a race with a buffer modification. Hold the trace_buffer

mutex to synchronise with any pending ring buffer order modification.

trace_buffer::subbuf_size is now actually useless, remove it. Also,

create accessors rb_subbuf_capacity() and rb_page_capacity() which

return the actual size available for storing events, while

rb_subbuf_size() returns the actual subbuf page-size.