CVE-2023-53368

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

tracing: Fix race issue between cpu buffer write and swap

Warning happened in rb_end_commit() at code: if (RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing)))

WARNING: CPU: 0 PID: 139 at kernel/trace/ring_buffer.c:3142 rb_commit+0x402/0x4a0 Call Trace: ring_buffer_unlock_commit+0x42/0x250 trace_buffer_unlock_commit_regs+0x3b/0x250 trace_event_buffer_commit+0xe5/0x440 trace_event_buffer_reserve+0x11c/0x150 trace_event_raw_event_sched_switch+0x23c/0x2c0 __traceiter_sched_switch+0x59/0x80 __schedule+0x72b/0x1580 schedule+0x92/0x120 worker_thread+0xa0/0x6f0

It is because the race between writing event into cpu buffer and swapping cpu buffer through file per_cpu/cpu0/snapshot:

Write on CPU 0 Swap buffer by per_cpu/cpu0/snapshot on CPU 1

                         tracing_snapshot_write()
                           [...]

ring_buffer_lock_reserve() cpu_buffer = buffer->buffers[cpu]; // 1. Suppose find 'cpu_buffer_a'; [...] rb_reserve_next_event() [...]

                           ring_buffer_swap_cpu()
                             if (local_read(&cpu_buffer_a->committing))
                                 goto out_dec;
                             if (local_read(&cpu_buffer_b->committing))
                                 goto out_dec;
                             buffer_a->buffers[cpu] = cpu_buffer_b;
                             buffer_b->buffers[cpu] = cpu_buffer_a;
                             // 2. cpu_buffer has swapped here.

  rb_start_commit(cpu_buffer);
  if (unlikely(READ_ONCE(cpu_buffer->buffer)
      != buffer)) { // 3. This check passed due to 'cpu_buffer->buffer'
    [...]           //    has not changed here.
    return NULL;
  }
                             cpu_buffer_b->buffer = buffer_a;
                             cpu_buffer_a->buffer = buffer_b;
                             [...]

  // 4. Reserve event from 'cpu_buffer_a'.

ring_buffer_unlock_commit() [...] cpu_buffer = buffer->buffers[cpu]; // 5. Now find 'cpu_buffer_b' !!! rb_commit(cpu_buffer) rb_end_commit() // 6. WARN for the wrong 'committing' state !!!

Based on above analysis, we can easily reproduce by following testcase:

#!/bin/bash

dmesg -n 7
sysctl -w kernel.panic_on_warn=1
TR=/sys/kernel/tracing
echo 7 > ${TR}/buffer_size_kb
echo "sched:sched_switch" > ${TR}/set_event
while [ true ]; do
        echo 1 > ${TR}/per_cpu/cpu0/snapshot
done &
while [ true ]; do
        echo 1 > ${TR}/per_cpu/cpu0/snapshot
done &
while [ true ]; do
        echo 1 > ${TR}/per_cpu/cpu0/snapshot
done &

To fix it, IIUC, we can use smp_call_function_single() to do the swap on the target cpu where the buffer is located, so that above race would be avoided.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.