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

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---