In the Linux kernel, the following vulnerability has been resolved: ring-buffer: Use...

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

ring-buffer: Use current_context for safe per-CPU buffer swap

The ring_buffer_swap_cpu() function currently checks the per-CPU committing counter to determine if a buffer is actively being written to before performing the swap. However, there exists a race window where this check can be bypassed:

ring_buffer_lock_reserve
    cpu_buffer = buffer->buffers[cpu];       // cpu_buffer_a
    rb_reserve_next_event
        rb_start_commit // inc committing
        if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {...}
        __rb_reserve_next
            rb_move_tail
                rb_end_commit(cpu_buffer);   // dec committing => 0
                /* interrupt hits here, successfully swaps! */
                local_inc(&cpu_buffer->committing);

ring_buffer_unlock_commit
    cpu_buffer = buffer->buffers[cpu];      // cpu_buffer_b
    rb_commit
        rb_end_commit
        RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing))
                                            // triggers warning

The committing counter can temporarily drop to 0 during a single write operation (within rb_move_tail), creating a window where swap can succeed even though the write is still in progress. This leads to inconsistent buffer state and triggers the RB_WARN_ON in rb_commit().

Replace the committing counter check with current_context checks, which are set at the entry of ring_buffer_lock_reserve() and remain valid throughout the entire write operation, providing a reliable indicator of buffer busy state during swap.