Forwarded: Re: [syzbot] [netfilter?] KASAN: use-after-free Read in nf_hook_entry_head

[syzbot]

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Subject: Re: [syzbot] [netfilter?] KASAN: use-after-free Read in nf_hook_entry_head
Author: koike@xxxxxxxxxx

#syz test

On 2/19/26 7:03 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4c51f90d45dc selftests/bpf: Add powerpc support for get_pr..
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1736f652580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6d9e410399043c26
> dashboard link: https://syzkaller.appspot.com/bug?extid=bb9127e278fa198e110c
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11213b3a580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/173ab67d0a10/disk-4c51f90d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/9c8787b7cc0e/vmlinux-4c51f90d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/bf9799a7764a/bzImage-4c51f90d.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+bb9127e278fa198e110c@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in read_pnet include/net/net_namespace.h:419 [inline]
> BUG: KASAN: use-after-free in dev_net include/linux/netdevice.h:2741 [inline]
> BUG: KASAN: use-after-free in nf_hook_entry_head+0x1f1/0x2c0 net/netfilter/core.c:319
> Read of size 8 at addr ffff88807c16c108 by task syz.3.29/6113
> 
> CPU: 0 UID: 0 PID: 6113 Comm: syz.3.29 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
> Call Trace:
>   <TASK>
>   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
>   read_pnet include/net/net_namespace.h:419 [inline]
>   dev_net include/linux/netdevice.h:2741 [inline]
>   nf_hook_entry_head+0x1f1/0x2c0 net/netfilter/core.c:319
>   __nf_unregister_net_hook+0x74/0x6f0 net/netfilter/core.c:491
>   nft_unregister_flowtable_ops net/netfilter/nf_tables_api.c:9059 [inline]
>   __nft_unregister_flowtable_net_hooks net/netfilter/nf_tables_api.c:9074 [inline]
>   __nft_release_hook net/netfilter/nf_tables_api.c:12063 [inline]
>   nft_rcv_nl_event+0x7b8/0xdb0 net/netfilter/nf_tables_api.c:12176
>   notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
>   blocking_notifier_call_chain+0x6a/0x90 kernel/notifier.c:380
>   netlink_release+0x123b/0x1ad0 net/netlink/af_netlink.c:761
>   __sock_release net/socket.c:662 [inline]
>   sock_close+0xc3/0x240 net/socket.c:1455
>   __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
> RIP: 0033:0x7f9f86f9c629
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc01263e28 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
> RAX: 0000000000000000 RBX: 00007f9f87217da0 RCX: 00007f9f86f9c629
> RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
> RBP: 00007f9f87217da0 R08: 00007f9f87216038 R09: 0000000000000000
> R10: 000000000003fd84 R11: 0000000000000246 R12: 000000000001a119
> R13: 00007f9f8721636c R14: 0000000000019ef5 R15: 00007ffc01263f30
>   </TASK>
> 
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88807c16e700 pfn:0x7c16c
> flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000000 ffffea000176ec08 ffff8880b8640a40 0000000000000000
> raw: ffff88807c16e700 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as freed
> page last allocated via order 2, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 6130, tgid 6113 (syz.3.29), ts 106243960748, free_ts 106536545080
>   set_page_owner include/linux/page_owner.h:32 [inline]
>   post_alloc_hook+0x231/0x280 mm/page_alloc.c:1888
>   prep_new_page mm/page_alloc.c:1896 [inline]
>   get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3961
>   __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5249
>   alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2485
>   ___kmalloc_large_node+0x4e/0x150 mm/slub.c:5118
>   __kmalloc_large_node_noprof+0x18/0x90 mm/slub.c:5149
>   __do_kmalloc_node mm/slub.c:5165 [inline]
>   __kvmalloc_node_noprof+0x7b/0x8a0 mm/slub.c:6668
>   alloc_netdev_mqs+0xa6/0x11b0 net/core/dev.c:12012
>   tun_set_iff+0x532/0xf00 drivers/net/tun.c:2778
>   __tun_chr_ioctl+0x7bb/0x1e10 drivers/net/tun.c:3088
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:597 [inline]
>   __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
>   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
> page last free pid 6113 tgid 6113 stack trace:
>   reset_page_owner include/linux/page_owner.h:25 [inline]
>   __free_pages_prepare mm/page_alloc.c:1432 [inline]
>   __free_frozen_pages+0xc00/0xd90 mm/page_alloc.c:2977
>   device_release+0x9e/0x1d0 drivers/base/core.c:-1
>   kobject_cleanup lib/kobject.c:689 [inline]
>   kobject_release lib/kobject.c:720 [inline]
>   kref_put include/linux/kref.h:65 [inline]
>   kobject_put+0x228/0x560 lib/kobject.c:737
>   netdev_run_todo+0xc75/0xde0 net/core/dev.c:11713
>   tun_detach drivers/net/tun.c:640 [inline]
>   tun_chr_close+0x13c/0x1c0 drivers/net/tun.c:3436
>   __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
> 
> Memory state around the buggy address:
>   ffff88807c16c000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>   ffff88807c16c080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> ffff88807c16c100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>                        ^
>   ffff88807c16c180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>   ffff88807c16c200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ==================================================================
> 
> 
> ---
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