Message-ID: <bec27999-93fa-49bf-86c2-1c6c007ccf35@kernel.org>
Date: Wed, 7 Jan 2026 17:50:54 +0800
From: Chao Yu <chao@...nel.org>
To: syzbot <syzbot+b4444e3c972a7a124187@...kaller.appspotmail.com>,
 linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Cc: chao@...nel.org
Subject: Re: [syzbot] [f2fs?] KASAN: use-after-free Read in f2fs_write_end_io
 (2)

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git bugfix/syzbot

On 12/22/2025 12:08 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    765b233a9b94 Merge tag 'i2c-for-6.19-rc2' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a56b1a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=513255d80ab78f2b
> dashboard link: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187
> 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=174b0b58580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162f8b1a580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-765b233a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f8288fd6c7cc/vmlinux-765b233a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/2a2ef1044b19/bzImage-765b233a.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/333719a5e15d/mount_1.gz
>    fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=17faddb4580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b4444e3c972a7a124187@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
> BUG: KASAN: slab-use-after-free in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
> BUG: KASAN: slab-use-after-free in get_pages fs/f2fs/f2fs.h:2718 [inline]
> BUG: KASAN: slab-use-after-free in f2fs_write_end_io+0x9b9/0xb60 fs/f2fs/data.c:364
> Read of size 4 at addr ffff88804357d170 by task kworker/u4:4/45
> 
> CPU: 0 UID: 0 PID: 45 Comm: kworker/u4:4 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
> Workqueue: loop0 loop_workfn
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0xe8/0x150 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
>   check_region_inline mm/kasan/generic.c:-1 [inline]
>   kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:200
>   instrument_atomic_read include/linux/instrumented.h:68 [inline]
>   atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
>   get_pages fs/f2fs/f2fs.h:2718 [inline]
>   f2fs_write_end_io+0x9b9/0xb60 fs/f2fs/data.c:364
>   blk_update_request+0x57e/0xe60 block/blk-mq.c:1007
>   blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1169
>   lo_rw_aio_complete drivers/block/loop.c:337 [inline]
>   lo_rw_aio+0xcd1/0xef0 drivers/block/loop.c:410
>   do_req_filebacked drivers/block/loop.c:-1 [inline]
>   loop_handle_cmd drivers/block/loop.c:1926 [inline]
>   loop_process_work+0x8fe/0x10b0 drivers/block/loop.c:1961
>   process_one_work kernel/workqueue.c:3257 [inline]
>   process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
>   worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
>   kthread+0x711/0x8a0 kernel/kthread.c:463
>   ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
>   </TASK>
> 
> Allocated by task 5484:
>   kasan_save_stack mm/kasan/common.c:56 [inline]
>   kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
>   poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
>   __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
>   kasan_kmalloc include/linux/kasan.h:262 [inline]
>   __kmalloc_cache_noprof+0x3e2/0x700 mm/slub.c:5776
>   kmalloc_noprof include/linux/slab.h:957 [inline]
>   kzalloc_noprof include/linux/slab.h:1094 [inline]
>   f2fs_fill_super+0x8c/0x6ec0 fs/f2fs/super.c:4895
>   get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
>   vfs_get_tree+0x92/0x2a0 fs/super.c:1751
>   fc_mount fs/namespace.c:1199 [inline]
>   do_new_mount_fc fs/namespace.c:3636 [inline]
>   do_new_mount+0x302/0xa10 fs/namespace.c:3712
>   do_mount fs/namespace.c:4035 [inline]
>   __do_sys_mount fs/namespace.c:4224 [inline]
>   __se_sys_mount+0x313/0x410 fs/namespace.c:4201
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 5484:
>   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:584
>   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:2540 [inline]
>   slab_free mm/slub.c:6670 [inline]
>   kfree+0x1c0/0x660 mm/slub.c:6878
>   kill_f2fs_super+0x5b6/0x6c0 fs/f2fs/super.c:5458
>   deactivate_locked_super+0xbc/0x130 fs/super.c:474
>   cleanup_mnt+0x425/0x4c0 fs/namespace.c:1318
>   task_work_run+0x1d4/0x260 kernel/task_work.c:233
>   exit_task_work include/linux/task_work.h:40 [inline]
>   do_exit+0x694/0x22f0 kernel/exit.c:971
>   do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
>   __do_sys_exit_group kernel/exit.c:1123 [inline]
>   __se_sys_exit_group kernel/exit.c:1121 [inline]
>   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1121
>   __pfx_syscall_get_nr+0x0/0x10 arch/x86/include/generated/asm/syscalls_64.h:232
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> 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:556
>   insert_work+0x3d/0x330 kernel/workqueue.c:2180
>   __queue_work+0xcd0/0xf90 kernel/workqueue.c:2335
>   queue_work_on+0x106/0x1c0 kernel/workqueue.c:2386
>   queue_work include/linux/workqueue.h:669 [inline]
>   schedule_work include/linux/workqueue.h:730 [inline]
>   f2fs_handle_critical_error+0x255/0x540 fs/f2fs/super.c:4624
>   f2fs_write_end_io+0x886/0xb60 fs/f2fs/data.c:351
>   __submit_merged_bio+0x256/0x660 fs/f2fs/data.c:540
>   __f2fs_submit_merged_write fs/f2fs/data.c:635 [inline]
>   __submit_merged_write_cond+0x471/0x530 fs/f2fs/data.c:657
>   f2fs_sync_node_pages+0x1479/0x15e0 fs/f2fs/node.c:2166
>   block_operations fs/f2fs/checkpoint.c:1276 [inline]
>   f2fs_write_checkpoint+0xdd5/0x2430 fs/f2fs/checkpoint.c:1678
>   kill_f2fs_super+0x2d2/0x6c0 fs/f2fs/super.c:5448
>   deactivate_locked_super+0xbc/0x130 fs/super.c:474
>   cleanup_mnt+0x425/0x4c0 fs/namespace.c:1318
>   task_work_run+0x1d4/0x260 kernel/task_work.c:233
>   exit_task_work include/linux/task_work.h:40 [inline]
>   do_exit+0x694/0x22f0 kernel/exit.c:971
>   do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
>   __do_sys_exit_group kernel/exit.c:1123 [inline]
>   __se_sys_exit_group kernel/exit.c:1121 [inline]
>   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1121
>   __pfx_syscall_get_nr+0x0/0x10 arch/x86/include/generated/asm/syscalls_64.h:232
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Second to 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:556
>   insert_work+0x3d/0x330 kernel/workqueue.c:2180
>   __queue_work+0xcd0/0xf90 kernel/workqueue.c:2335
>   queue_work_on+0x106/0x1c0 kernel/workqueue.c:2386
>   sanity_check_node_footer fs/f2fs/node.c:1536 [inline]
>   __get_node_folio+0xcaf/0x14f0 fs/f2fs/node.c:1581
>   do_read_inode fs/f2fs/inode.c:425 [inline]
>   f2fs_iget+0x77c/0x5640 fs/f2fs/inode.c:596
>   f2fs_nfs_get_inode+0x76/0x110 fs/f2fs/super.c:3723
>   generic_fh_to_dentry+0x9f/0xf0 fs/libfs.c:1498
>   exportfs_decode_fh_raw+0x178/0x6e0 fs/exportfs/expfs.c:456
>   do_handle_to_path+0xa4/0x1a0 fs/fhandle.c:276
>   handle_to_path fs/fhandle.c:400 [inline]
>   do_handle_open+0x6a1/0x930 fs/fhandle.c:424
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The buggy address belongs to the object at ffff88804357c000
>   which belongs to the cache kmalloc-8k of size 8192
> The buggy address is located 4464 bytes inside of
>   freed 8192-byte region [ffff88804357c000, ffff88804357e000)
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x43578
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 04fff00000000040 ffff88801a442280 ffffea000046b000 0000000000000002
> raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
> head: 04fff00000000040 ffff88801a442280 ffffea000046b000 0000000000000002
> head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
> head: 04fff00000000003 ffffea00010d5e01 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 0x528c0(GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NORETRY|__GFP_COMP), pid 5411, tgid 5411 (syz-executor), ts 97414573985, free_ts 95403368329
>   set_page_owner include/linux/page_owner.h:32 [inline]
>   post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
>   prep_new_page mm/page_alloc.c:1854 [inline]
>   get_page_from_freelist+0x24e0/0x2580 mm/page_alloc.c:3915
>   __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
>   alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
>   alloc_slab_page mm/slub.c:3075 [inline]
>   allocate_slab+0x86/0x3b0 mm/slub.c:3248
>   new_slab mm/slub.c:3302 [inline]
>   ___slab_alloc+0xe53/0x1820 mm/slub.c:4656
>   __slab_alloc+0x65/0x100 mm/slub.c:4779
>   __slab_alloc_node mm/slub.c:4855 [inline]
>   slab_alloc_node mm/slub.c:5251 [inline]
>   __do_kmalloc_node mm/slub.c:5656 [inline]
>   __kvmalloc_node_noprof+0x6b6/0x920 mm/slub.c:7136
>   kvmalloc_array_node_noprof include/linux/slab.h:1122 [inline]
>   __ptr_ring_init_queue_alloc_noprof include/linux/ptr_ring.h:481 [inline]
>   ptr_ring_init_noprof include/linux/ptr_ring.h:499 [inline]
>   wg_packet_queue_init+0xbc/0x320 drivers/net/wireguard/queueing.c:32
>   wg_newlink+0x2f6/0x670 drivers/net/wireguard/device.c:352
>   rtnl_newlink_create+0x310/0xb00 net/core/rtnetlink.c:3840
>   __rtnl_newlink net/core/rtnetlink.c:3957 [inline]
>   rtnl_newlink+0x16e7/0x1c90 net/core/rtnetlink.c:4072
>   rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6958
>   netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
>   netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
>   netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
>   netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
> page last free pid 4363 tgid 4363 stack trace:
>   reset_page_owner include/linux/page_owner.h:25 [inline]
>   free_pages_prepare mm/page_alloc.c:1395 [inline]
>   __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
>   unix_net_exit+0x6b/0xb0 net/unix/af_unix.c:3837
>   ops_exit_list net/core/net_namespace.c:199 [inline]
>   ops_undo_list+0x49a/0x990 net/core/net_namespace.c:252
>   cleanup_net+0x4d8/0x7a0 net/core/net_namespace.c:696
>   process_one_work kernel/workqueue.c:3257 [inline]
>   process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
>   worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
>   kthread+0x711/0x8a0 kernel/kthread.c:463
>   ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
> 
> Memory state around the buggy address:
>   ffff88804357d000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff88804357d080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff88804357d100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                               ^
>   ffff88804357d180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff88804357d200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> 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.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup

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