CVE-2026-74601

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/26662bc8fced1d668fa1aa146eda085bfc67bd0b
• https://git.kernel.org/stable/c/6b524e6b234e45c7f5f90d13b042c6f57f80105c
• https://git.kernel.org/stable/c/597f279b7b4a06412e3d965e98cc36e181cdbede
• https://git.kernel.org/stable/c/22709117d9ae95e52673685f98caac7c356a8227
• https://git.kernel.org/stable/c/ad7e10c7ea89af45ac1bf1814855d45da472703d
• https://git.kernel.org/stable/c/5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f
• https://git.kernel.org/stable/c/5e6e2a18c20e88167d414f666032792e8bf19b80
• https://git.kernel.org/stable/c/f27bdc43077e4fcb5557dfc315ee8d91e741f483

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