bpf: Fix a race condition between btf_put() and map_free()
CVE: CVE-2023-52446
Component: kernel
Severity: Low
CVSS v3: 4.2/AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L
Release date: 2023-01-01T00:00:00+00:00

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

bpf: Fix a race condition between btf_put() and map_free()

When running `./test_progs -j` in my local vm with latest kernel,
I once hit a kasan error like below:

  [ 1887.184724] BUG: KASAN: slab-use-after-free in bpf_rb_root_free+0x1f8/0x2b0
  [ 1887.185599] Read of size 4 at addr ffff888106806910 by task kworker/u12:2/2830
  [ 1887.186498]
  [ 1887.186712] CPU: 3 PID: 2830 Comm: kworker/u12:2 Tainted: G           OEL     6.7.0-rc3-00699-g90679706d486-dirty #494
  [ 1887.188034] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
  [ 1887.189618] Workqueue: events_unbound bpf_map_free_deferred
  [ 1887.190341] Call Trace:
  [ 1887.190666]  <TASK>
  [ 1887.190949]  dump_stack_lvl+0xac/0xe0
  [ 1887.191423]  ? nf_tcp_handle_invalid+0x1b0/0x1b0
  [ 1887.192019]  ? panic+0x3c0/0x3c0
  [ 1887.192449]  print_report+0x14f/0x720
  [ 1887.192930]  ? preempt_count_sub+0x1c/0xd0
  [ 1887.193459]  ? __virt_addr_valid+0xac/0x120
  [ 1887.194004]  ? bpf_rb_root_free+0x1f8/0x2b0
  [ 1887.194572]  kasan_report+0xc3/0x100
  [ 1887.195085]  ? bpf_rb_root_free+0x1f8/0x2b0
  [ 1887.195668]  bpf_rb_root_free+0x1f8/0x2b0
  [ 1887.196183]  ? __bpf_obj_drop_impl+0xb0/0xb0
  [ 1887.196736]  ? preempt_count_sub+0x1c/0xd0
  [ 1887.197270]  ? preempt_count_sub+0x1c/0xd0
  [ 1887.197802]  ? _raw_spin_unlock+0x1f/0x40
  [ 1887.198319]  bpf_obj_free_fields+0x1d4/0x260
  [ 1887.198883]  array_map_free+0x1a3/0x260
  [ 1887.199380]  bpf_map_free_deferred+0x7b/0xe0
  [ 1887.199943]  process_scheduled_works+0x3a2/0x6c0
  [ 1887.200549]  worker_thread+0x633/0x890
  [ 1887.201047]  ? __kthread_parkme+0xd7/0xf0
  [ 1887.201574]  ? kthread+0x102/0x1d0
  [ 1887.202020]  kthread+0x1ab/0x1d0
  [ 1887.202447]  ? pr_cont_work+0x270/0x270
  [ 1887.202954]  ? kthread_blkcg+0x50/0x50
  [ 1887.203444]  ret_from_fork+0x34/0x50
  [ 1887.203914]  ? kthread_blkcg+0x50/0x50
  [ 1887.204397]  ret_from_fork_asm+0x11/0x20
  [ 1887.204913]  </TASK>
  [ 1887.204913]  </TASK>
  [ 1887.205209]
  [ 1887.205416] Allocated by task 2197:
  [ 1887.205881]  kasan_set_track+0x3f/0x60
  [ 1887.206366]  __kasan_kmalloc+0x6e/0x80
  [ 1887.206856]  __kmalloc+0xac/0x1a0
  [ 1887.207293]  btf_parse_fields+0xa15/0x1480
  [ 1887.207836]  btf_parse_struct_metas+0x566/0x670
  [ 1887.208387]  btf_new_fd+0x294/0x4d0
  [ 1887.208851]  __sys_bpf+0x4ba/0x600
  [ 1887.209292]  __x64_sys_bpf+0x41/0x50
  [ 1887.209762]  do_syscall_64+0x4c/0xf0
  [ 1887.210222]  entry_SYSCALL_64_after_hwframe+0x63/0x6b
  [ 1887.210868]
  [ 1887.211074] Freed by task 36:
  [ 1887.211460]  kasan_set_track+0x3f/0x60
  [ 1887.211951]  kasan_save_free_info+0x28/0x40
  [ 1887.212485]  ____kasan_slab_free+0x101/0x180
  [ 1887.213027]  __kmem_cache_free+0xe4/0x210
  [ 1887.213514]  btf_free+0x5b/0x130
  [ 1887.213918]  rcu_core+0x638/0xcc0
  [ 1887.214347]  __do_softirq+0x114/0x37e

The error happens at bpf_rb_root_free+0x1f8/0x2b0:

  00000000000034c0 <bpf_rb_root_free>:
  ; {
    34c0: f3 0f 1e fa                   endbr64
    34c4: e8 00 00 00 00                callq   0x34c9 <bpf_rb_root_free+0x9>
    34c9: 55                            pushq   %rbp
    34ca: 48 89 e5                      movq    %rsp, %rbp
  ...
  ;       if (rec && rec->refcount_off >= 0 &&
    36aa: 4d 85 ed                      testq   %r13, %r13
    36ad: 74 a9                         je      0x3658 <bpf_rb_root_free+0x198>
    36af: 49 8d 7d 10                   leaq    0x10(%r13), %rdi
    36b3: e8 00 00 00 00                callq   0x36b8 <bpf_rb_root_free+0x1f8>
                                        <==== kasan function
    36b8: 45 8b 7d 10                   movl    0x10(%r13), %r15d
                                        <==== use-after-free load
    36bc: 45 85 ff                      testl   %r15d, %r15d
    36bf: 78 8c                         js      0x364d <bpf_rb_root_free+0x18d>

So the problem 
---truncated---


Remediation:
No mitigation is currently available for this vulnerability. Make sure to perform the updates as they become available.