Race Condition Affecting kernel-zfcpdump-devel package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-zfcpdump-devel package and not the kernel-zfcpdump-devel package as distributed by RHEL. See How to fix? for RHEL:9 relevant fixed versions and status.

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.

• https://access.redhat.com/security/cve/CVE-2023-53368
• https://git.kernel.org/stable/c/3163f635b20e9e1fb4659e74f47918c9dddfe64e
• https://git.kernel.org/stable/c/37ca1b686078b00cc4ffa008e2190615f7709b5d
• https://git.kernel.org/stable/c/6182318ac04648b46db9d441fd7d696337fcdd0b
• https://git.kernel.org/stable/c/74c85396bd73eca80b96510b4edf93b9a3aff75f
• https://git.kernel.org/stable/c/89c89da92a60028013f9539be0dcce7e44405a43
• https://git.kernel.org/stable/c/90e037cabc2c2dfc39b3dd9c5b22ea91f995539a
• https://git.kernel.org/stable/c/c5d30d6aa83d99fba8dfdd9cf6c4e4e7a63244db