Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in list_lru_del

On Fri, 28 Nov 2025 13:46:26 -0800 syzbot <[email protected]> wrote:

> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    e538109ac71d Merge tag 'drm-fixes-2025-11-28' of https://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10fd2112580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a1db0fea040c2a9f
> dashboard link: https://syzkaller.appspot.com/bug?extid=6663075ddb9be85fa6e5
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12fd2112580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15a10112580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-e538109a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3cf595fe0afc/vmlinux-e538109a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/e6e26f95e409/bzImage-e538109a.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/445f48d13fdb/mount_7.gz
>   fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=11a10112580000)
> 
> The issue was bisected to:
> 
> commit 14152654805256d760315ec24e414363bfa19a06
> Author: Kent Overstreet <[email protected]>
> Date:   Mon Nov 25 05:21:27 2024 +0000
> 
>     bcachefs: Bad btree roots are now autofix
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=108d43a8580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=128d43a8580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=148d43a8580000

Thanks.

Bisection obviously went wrong.

I'll cc the gfs2 list.

> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
> Fixes: 141526548052 ("bcachefs: Bad btree roots are now autofix")
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0xb5/0x190 lib/list_debug.c:65
> Read of size 8 at addr ffff88800098a080 by task syz.0.17/5483
> 
> CPU: 0 UID: 0 PID: 5483 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:378 [inline]
>  print_report+0xca/0x240 mm/kasan/report.c:482
>  kasan_report+0x118/0x150 mm/kasan/report.c:595
>  __list_del_entry_valid_or_report+0xb5/0x190 lib/list_debug.c:65
>  __list_del_entry_valid include/linux/list.h:132 [inline]
>  __list_del_entry include/linux/list.h:223 [inline]
>  list_del_init include/linux/list.h:295 [inline]
>  list_lru_del+0x98/0x210 mm/list_lru.c:210
>  gfs2_quota_cleanup+0x21e/0x6f0 fs/gfs2/quota.c:1532
>  gfs2_make_fs_ro+0x27a/0x300 fs/gfs2/super.c:566
>  gfs2_put_super+0x224/0x950 fs/gfs2/super.c:598
>  generic_shutdown_super+0x135/0x2c0 fs/super.c:642
>  kill_block_super+0x44/0x90 fs/super.c:1729
>  deactivate_locked_super+0xbc/0x130 fs/super.c:473
>  cleanup_mnt+0x425/0x4c0 fs/namespace.c:1318
>  task_work_run+0x1d4/0x260 kernel/task_work.c:227
>  exit_task_work include/linux/task_work.h:40 [inline]
>  do_exit+0x6b5/0x2300 kernel/exit.c:966
>  do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
>  __do_sys_exit_group kernel/exit.c:1118 [inline]
>  __se_sys_exit_group kernel/exit.c:1116 [inline]
>  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1116
>  x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f4bb3d8f7c9
> Code: Unable to access opcode bytes at 0x7f4bb3d8f79f.
> RSP: 002b:00007ffd56395328 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4bb3d8f7c9
> RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000003 R08: 0000001d5639541f R09: 00007f4bb3fb4280
> R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f4bb3fb4280 R14: 0000000000000003 R15: 00007ffd563953e0
>  </TASK>
> 
> Allocated by task 5483:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  unpoison_slab_object mm/kasan/common.c:342 [inline]
>  __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:368
>  kasan_slab_alloc include/linux/kasan.h:252 [inline]
>  slab_post_alloc_hook mm/slub.c:4978 [inline]
>  slab_alloc_node mm/slub.c:5288 [inline]
>  kmem_cache_alloc_noprof+0x367/0x6e0 mm/slub.c:5295
>  qd_alloc+0x50/0x250 fs/gfs2/quota.c:234
>  gfs2_quota_init+0x762/0x1200 fs/gfs2/quota.c:1448
>  gfs2_make_fs_rw+0x181/0x2b0 fs/gfs2/super.c:149
>  gfs2_fill_super+0x1a7b/0x20d0 fs/gfs2/ops_fstype.c:1280
>  get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1698
>  gfs2_get_tree+0x51/0x1e0 fs/gfs2/ops_fstype.c:1337
>  vfs_get_tree+0x92/0x2b0 fs/super.c:1758
>  fc_mount fs/namespace.c:1199 [inline]
>  do_new_mount_fc fs/namespace.c:3642 [inline]
>  do_new_mount+0x302/0xa10 fs/namespace.c:3718
>  do_mount fs/namespace.c:4041 [inline]
>  __do_sys_mount fs/namespace.c:4229 [inline]
>  __se_sys_mount+0x313/0x410 fs/namespace.c:4206
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 15:
>  kasan_save_stack mm/kasan/common.c:56 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>  __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587
>  kasan_save_free_info mm/kasan/kasan.h:406 [inline]
>  poison_slab_object mm/kasan/common.c:252 [inline]
>  __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
>  kasan_slab_free include/linux/kasan.h:234 [inline]
>  slab_free_hook mm/slub.c:2543 [inline]
>  slab_free mm/slub.c:6642 [inline]
>  kmem_cache_free+0x19b/0x690 mm/slub.c:6752
>  gfs2_qd_dealloc+0x70/0xe0 fs/gfs2/quota.c:111
>  rcu_do_batch kernel/rcu/tree.c:2605 [inline]
>  rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
>  handle_softirqs+0x286/0x870 kernel/softirq.c:622
>  run_ksoftirqd+0x9b/0x100 kernel/softirq.c:1063
>  smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
>  kthread+0x711/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x4bc/0x870 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:56
>  kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:559
>  __call_rcu_common kernel/rcu/tree.c:3123 [inline]
>  call_rcu+0x157/0x9c0 kernel/rcu/tree.c:3243
>  gfs2_quota_sync+0x3c4/0x460 fs/gfs2/quota.c:1361
>  gfs2_sync_fs+0x4c/0xb0 fs/gfs2/super.c:658
>  sync_filesystem+0xee/0x230 fs/sync.c:56
>  generic_shutdown_super+0x6f/0x2c0 fs/super.c:621
>  kill_block_super+0x44/0x90 fs/super.c:1729
>  deactivate_locked_super+0xbc/0x130 fs/super.c:473
>  cleanup_mnt+0x425/0x4c0 fs/namespace.c:1318
>  task_work_run+0x1d4/0x260 kernel/task_work.c:227
>  exit_task_work include/linux/task_work.h:40 [inline]
>  do_exit+0x6b5/0x2300 kernel/exit.c:966
>  do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
>  __do_sys_exit_group kernel/exit.c:1118 [inline]
>  __se_sys_exit_group kernel/exit.c:1116 [inline]
>  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1116
>  x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The buggy address belongs to the object at ffff88800098a000
>  which belongs to the cache gfs2_quotad of size 272
> The buggy address is located 128 bytes inside of
>  freed 272-byte region [ffff88800098a000, ffff88800098a110)
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x98a
> flags: 0x7ff00000000000(node=0|zone=0|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 007ff00000000000 ffff888032687dc0 dead000000000122 0000000000000000
> raw: 0000000000000000 00000000800c000c 00000000f5000000 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Reclaimable, gfp_mask 0x52c50(GFP_NOFS|__GFP_RECLAIMABLE|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5483, tgid 5483 (syz.0.17), ts 105510017652, free_ts 102275632308
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x234/0x290 mm/page_alloc.c:1845
>  prep_new_page mm/page_alloc.c:1853 [inline]
>  get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3879
>  __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5178
>  alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
>  alloc_slab_page mm/slub.c:3059 [inline]
>  allocate_slab+0x96/0x350 mm/slub.c:3232
>  new_slab mm/slub.c:3286 [inline]
>  ___slab_alloc+0xf56/0x1990 mm/slub.c:4655
>  __slab_alloc+0x65/0x100 mm/slub.c:4778
>  __slab_alloc_node mm/slub.c:4854 [inline]
>  slab_alloc_node mm/slub.c:5276 [inline]
>  kmem_cache_alloc_noprof+0x3f9/0x6e0 mm/slub.c:5295
>  qd_alloc+0x50/0x250 fs/gfs2/quota.c:234
>  gfs2_quota_init+0x762/0x1200 fs/gfs2/quota.c:1448
>  gfs2_make_fs_rw+0x181/0x2b0 fs/gfs2/super.c:149
>  gfs2_fill_super+0x1a7b/0x20d0 fs/gfs2/ops_fstype.c:1280
>  get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1698
>  gfs2_get_tree+0x51/0x1e0 fs/gfs2/ops_fstype.c:1337
>  vfs_get_tree+0x92/0x2b0 fs/super.c:1758
>  fc_mount fs/namespace.c:1199 [inline]
>  do_new_mount_fc fs/namespace.c:3642 [inline]
>  do_new_mount+0x302/0xa10 fs/namespace.c:3718
> page last free pid 5433 tgid 5433 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  free_pages_prepare mm/page_alloc.c:1394 [inline]
>  free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:2958
>  folios_put_refs+0x584/0x670 mm/swap.c:1002
>  free_pages_and_swap_cache+0x4be/0x520 mm/swap_state.c:358
>  __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
>  tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
>  tlb_flush_mmu_free mm/mmu_gather.c:397 [inline]
>  tlb_flush_mmu+0x3a0/0x680 mm/mmu_gather.c:404
>  tlb_finish_mmu+0xc3/0x1d0 mm/mmu_gather.c:497
>  exit_mmap+0x444/0xb40 mm/mmap.c:1293
>  __mmput+0x118/0x430 kernel/fork.c:1133
>  exit_mm+0x1da/0x2c0 kernel/exit.c:582
>  do_exit+0x648/0x2300 kernel/exit.c:954
>  do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
>  __do_sys_exit_group kernel/exit.c:1118 [inline]
>  __se_sys_exit_group kernel/exit.c:1116 [inline]
>  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1116
>  x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Memory state around the buggy address:
>  ffff888000989f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>  ffff88800098a000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff88800098a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffff88800098a100: fb fb fc fc fc fc fc fc fc fc 00 00 00 00 00 00
>  ffff88800098a180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ==================================================================
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.