Forwarded: Re: [syzbot ci] Re: Close race in freeing special fields and map value

[syzbot <syzbot@syzkaller.appspotmail.com>]

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Subject: Re: [syzbot ci] Re: Close race in freeing special fields and map value
Author: memxor@gmail.com

#syz test: https://github.com/kkdwvd/linux dtor

On Thu, 26 Feb 2026 at 10:31, syzbot ci
<syzbot+ci3826af8b4f91bf97@syzkaller.appspotmail.com> wrote:
>
> syzbot ci has tested the following series
>
> [v1] Close race in freeing special fields and map value
> https://lore.kernel.org/all/20260225185121.2057388-1-memxor@gmail.com
> * [PATCH bpf-next v1 1/4] bpf: Register dtor for freeing special fields
> * [PATCH bpf-next v1 2/4] bpf: Delay freeing fields in local storage
> * [PATCH bpf-next v1 3/4] bpf: Retire rcu_trace_implies_rcu_gp() from local storage
> * [PATCH bpf-next v1 4/4] selftests/bpf: Add tests for special fields races
>
> and found the following issue:
> KASAN: slab-use-after-free Read in free_all
>
> Full report is available here:
> https://ci.syzbot.org/series/ad9c7ce6-d861-4afe-821a-e8fae6120b12
>
> ***
>
> KASAN: slab-use-after-free Read in free_all
>
> tree:      bpf-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/bpf/bpf-next.git
> base:      f620af11c27b8ec9994a39fe968aa778112d1566
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/b2735b0b-963d-41a7-bb33-db10494a24e1/config
> syz repro: https://ci.syzbot.org/findings/3ee61f99-7d80-4986-a0b1-492ffb6b1c46/syz_repro
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in free_all+0x84/0x140 kernel/bpf/memalloc.c:271
> Read of size 8 at addr ffff888112ee9260 by task swapper/0/0
>
> CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
>  <IRQ>
>  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:378 [inline]
>  print_report+0xba/0x230 mm/kasan/report.c:482
>  kasan_report+0x117/0x150 mm/kasan/report.c:595
>  free_all+0x84/0x140 kernel/bpf/memalloc.c:271
>  do_call_rcu_ttrace+0x385/0x400 kernel/bpf/memalloc.c:315
>  __free_by_rcu+0x23b/0x3f0 kernel/bpf/memalloc.c:381
>  rcu_do_batch kernel/rcu/tree.c:2617 [inline]
>  rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
>  handle_softirqs+0x22a/0x870 kernel/softirq.c:622
>  __do_softirq kernel/softirq.c:656 [inline]
>  invoke_softirq kernel/softirq.c:496 [inline]
>  __irq_exit_rcu+0x5f/0x150 kernel/softirq.c:723
>  irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
>  instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
>  sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1056
>  </IRQ>
>  <TASK>
>  asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
> RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
> Code: 8e 6d 02 c3 cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 43 3d 1c 00 fb f4 <e9> 7c ea 02 00 cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
> RSP: 0018:ffffffff8e407dc0 EFLAGS: 00000202
> RAX: 00000000000d2297 RBX: ffffffff819a80ad RCX: 0000000080000001
> RDX: 0000000000000001 RSI: ffffffff8def22fa RDI: ffffffff8c27a800
> RBP: ffffffff8e407eb0 R08: ffff88812103395b R09: 1ffff1102420672b
> R10: dffffc0000000000 R11: ffffed102420672c R12: ffffffff90117db0
> R13: 1ffffffff1c929d8 R14: 0000000000000000 R15: 0000000000000000
>  arch_safe_halt arch/x86/kernel/process.c:766 [inline]
>  default_idle+0x9/0x20 arch/x86/kernel/process.c:767
>  default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
>  cpuidle_idle_call kernel/sched/idle.c:191 [inline]
>  do_idle+0x1bd/0x500 kernel/sched/idle.c:332
>  cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:430
>  rest_init+0x2de/0x300 init/main.c:760
>  start_kernel+0x385/0x3d0 init/main.c:1210
>  x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
>  x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
>  common_startup_64+0x13e/0x147
>  </TASK>
>
> Allocated by task 5961:
>  kasan_save_stack mm/kasan/common.c:57 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
>  poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
>  kasan_kmalloc include/linux/kasan.h:263 [inline]
>  __do_kmalloc_node mm/slub.c:5219 [inline]
>  __kmalloc_node_noprof+0x4e0/0x7c0 mm/slub.c:5225
>  kmalloc_node_noprof include/linux/slab.h:1093 [inline]
>  __bpf_map_area_alloc kernel/bpf/syscall.c:398 [inline]
>  bpf_map_area_alloc+0x64/0x170 kernel/bpf/syscall.c:411
>  trie_alloc+0x14f/0x340 kernel/bpf/lpm_trie.c:588
>  map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1507
>  __sys_bpf+0x6e1/0x950 kernel/bpf/syscall.c:6210
>  __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
>  __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6339
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 83:
>  kasan_save_stack mm/kasan/common.c:57 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
>  poison_slab_object mm/kasan/common.c:253 [inline]
>  __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
>  kasan_slab_free include/linux/kasan.h:235 [inline]
>  slab_free_hook mm/slub.c:2687 [inline]
>  slab_free mm/slub.c:6124 [inline]
>  kfree+0x1c1/0x630 mm/slub.c:6442
>  bpf_map_free kernel/bpf/syscall.c:892 [inline]
>  bpf_map_free_deferred+0x217/0x460 kernel/bpf/syscall.c:919
>  process_one_work kernel/workqueue.c:3275 [inline]
>  process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
>  worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
>  kthread+0x388/0x470 kernel/kthread.c:467
>  ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> Last potentially related work creation:
>  kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
>  kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
>  insert_work+0x3d/0x330 kernel/workqueue.c:2199
>  __queue_work+0xd03/0x1020 kernel/workqueue.c:2354
>  queue_work_on+0x106/0x1d0 kernel/workqueue.c:2405
>  bpf_map_put_with_uref kernel/bpf/syscall.c:975 [inline]
>  bpf_map_release+0x127/0x140 kernel/bpf/syscall.c:985
>  __fput+0x44f/0xa70 fs/file_table.c:469
>  task_work_run+0x1d9/0x270 kernel/task_work.c:233
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
>  exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
>  __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
>  syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
>  do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> The buggy address belongs to the object at ffff888112ee9000
>  which belongs to the cache kmalloc-cg-1k of size 1024
> The buggy address is located 608 bytes inside of
>  freed 1024-byte region [ffff888112ee9000, ffff888112ee9400)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x112ee8
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> memcg:ffff888106b17c01
> flags: 0x17ff00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 017ff00000000040 ffff88810005d280 dead000000000100 dead000000000122
> raw: 0000000000000000 0000000800100010 00000000f5000000 ffff888106b17c01
> head: 017ff00000000040 ffff88810005d280 dead000000000100 dead000000000122
> head: 0000000000000000 0000000800100010 00000000f5000000 ffff888106b17c01
> head: 017ff00000000003 ffffea00044bba01 00000000ffffffff 00000000ffffffff
> head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5550, tgid 5550 (dhcpcd), ts 37867090520, free_ts 37834172120
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
>  prep_new_page mm/page_alloc.c:1897 [inline]
>  get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
>  __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
>  alloc_slab_page mm/slub.c:3255 [inline]
>  allocate_slab+0x77/0x660 mm/slub.c:3444
>  new_slab mm/slub.c:3502 [inline]
>  refill_objects+0x331/0x3c0 mm/slub.c:7134
>  refill_sheaf mm/slub.c:2804 [inline]
>  __pcs_replace_empty_main+0x2b9/0x620 mm/slub.c:4578
>  alloc_from_pcs mm/slub.c:4681 [inline]
>  slab_alloc_node mm/slub.c:4815 [inline]
>  __do_kmalloc_node mm/slub.c:5218 [inline]
>  __kmalloc_node_track_caller_noprof+0x572/0x7b0 mm/slub.c:5327
>  kmalloc_reserve net/core/skbuff.c:635 [inline]
>  __alloc_skb+0x2c1/0x7d0 net/core/skbuff.c:713
>  alloc_skb include/linux/skbuff.h:1383 [inline]
>  alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6750
>  sock_alloc_send_pskb+0x878/0x990 net/core/sock.c:2995
>  unix_dgram_sendmsg+0x460/0x18e0 net/unix/af_unix.c:2125
>  sock_sendmsg_nosec net/socket.c:727 [inline]
>  __sock_sendmsg net/socket.c:742 [inline]
>  sock_write_iter+0x503/0x550 net/socket.c:1195
>  do_iter_readv_writev+0x619/0x8c0 fs/read_write.c:-1
>  vfs_writev+0x33c/0x990 fs/read_write.c:1059
>  do_writev+0x154/0x2e0 fs/read_write.c:1105
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
> page last free pid 5678 tgid 5678 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  __free_pages_prepare mm/page_alloc.c:1433 [inline]
>  __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
>  __slab_free+0x263/0x2b0 mm/slub.c:5532
>  qlink_free mm/kasan/quarantine.c:163 [inline]
>  qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
>  kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
>  __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
>  kasan_slab_alloc include/linux/kasan.h:253 [inline]
>  slab_post_alloc_hook mm/slub.c:4501 [inline]
>  slab_alloc_node mm/slub.c:4830 [inline]
>  __do_kmalloc_node mm/slub.c:5218 [inline]
>  __kmalloc_noprof+0x316/0x760 mm/slub.c:5231
>  kmalloc_noprof include/linux/slab.h:966 [inline]
>  tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
>  tomoyo_realpath_nofollow+0xc3/0x110 security/tomoyo/realpath.c:304
>  tomoyo_find_next_domain+0x259/0x1aa0 security/tomoyo/domain.c:731
>  tomoyo_bprm_check_security+0x11b/0x180 security/tomoyo/tomoyo.c:102
>  security_bprm_check+0x85/0x240 security/security.c:794
>  search_binary_handler fs/exec.c:1654 [inline]
>  exec_binprm fs/exec.c:1696 [inline]
>  bprm_execve+0x896/0x1460 fs/exec.c:1748
>  do_execveat_common+0x50d/0x690 fs/exec.c:1846
>  __do_sys_execve fs/exec.c:1930 [inline]
>  __se_sys_execve fs/exec.c:1924 [inline]
>  __x64_sys_execve+0x97/0xc0 fs/exec.c:1924
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Memory state around the buggy address:
>  ffff888112ee9100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888112ee9180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff888112ee9200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                        ^
>  ffff888112ee9280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888112ee9300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> ----------------
> Code disassembly (best guess):
>    0:   8e 6d 02                mov    0x2(%rbp),%gs
>    3:   c3                      ret
>    4:   cc                      int3
>    5:   cc                      int3
>    6:   cc                      int3
>    7:   cc                      int3
>    8:   cc                      int3
>    9:   cc                      int3
>    a:   cc                      int3
>    b:   90                      nop
>    c:   90                      nop
>    d:   90                      nop
>    e:   90                      nop
>    f:   90                      nop
>   10:   90                      nop
>   11:   90                      nop
>   12:   90                      nop
>   13:   90                      nop
>   14:   90                      nop
>   15:   90                      nop
>   16:   90                      nop
>   17:   90                      nop
>   18:   90                      nop
>   19:   90                      nop
>   1a:   90                      nop
>   1b:   f3 0f 1e fa             endbr64
>   1f:   eb 07                   jmp    0x28
>   21:   0f 00 2d 43 3d 1c 00    verw   0x1c3d43(%rip)        # 0x1c3d6b
>   28:   fb                      sti
>   29:   f4                      hlt
> * 2a:   e9 7c ea 02 00          jmp    0x2eaab <-- trapping instruction
>   2f:   cc                      int3
>   30:   cc                      int3
>   31:   cc                      int3
>   32:   cc                      int3
>   33:   cc                      int3
>   34:   cc                      int3
>   35:   cc                      int3
>   36:   cc                      int3
>   37:   cc                      int3
>   38:   cc                      int3
>   39:   cc                      int3
>   3a:   cc                      int3
>   3b:   90                      nop
>   3c:   90                      nop
>   3d:   90                      nop
>   3e:   90                      nop
>   3f:   90                      nop
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: syzbot@syzkaller.appspotmail.com
>
> ---
> This report is generated by a bot. It may contain errors.
> syzbot ci engineers can be reached at syzkaller@googlegroups.com.