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

syzbot
2026-03-04T15:34:03Z

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in nf_hook_entry_head

nft_flowtable_event: unregistering device syzkaller0@ffff888032578000 with flowtable @ffff888034ecd000
==================================================================
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 ffff888032578108 by task syz.0.299/7219

CPU: 1 UID: 0 PID: 7219 Comm: syz.0.299 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:12068 [inline]
nft_rcv_nl_event+0x7b8/0xdb0 net/netfilter/nf_tables_api.c:12181
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: 0033:0x7fb92579c629
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:00007ffd8c9aa7a8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffd8c9aa890 RCX: 00007fb92579c629
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 000000000002c7b9 R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b30f20000 R11: 0000000000000246 R12: 00007ffd8c9aa8d0
R13: 00007fb925a1609c R14: 000000000002c7ee R15: 00007fb925a16090
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888032578000 pfn:0x32578
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00019f1008 ffff8880b8740a40 0000000000000000
raw: ffff888032578000 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 7221, tgid 7219 (syz.0.299), ts 182259395299, free_ts 182346434698
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 7219 tgid 7219 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:
ffff888032578000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888032578080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888032578100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888032578180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888032578200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Tested on:

commit: 4c51f90d selftests/bpf: Add powerpc support for get_pr..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=150f1e4a580000
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
patch: https://syzkaller.appspot.com/x/patch.diff?x=12fef0ba580000