==================================================================
BUG: KASAN: out-of-bounds in hlist_add_head include/linux/list.h:814 [inline]
BUG: KASAN: out-of-bounds in enqueue_timer+0x9e/0x2c0 kernel/time/timer.c:541
Write of size 8 at addr ffff8881e86231c8 by task syz.3.176/1044

CPU: 0 PID: 1044 Comm: syz.3.176 Not tainted 5.4.292-syzkaller-00021-gcd8e74fa0fa3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 __dump_stack+0x1e/0x20 lib/dump_stack.c:77
 dump_stack+0x15b/0x1b8 lib/dump_stack.c:118
 print_address_description+0x8d/0x4c0 mm/kasan/report.c:384
 __kasan_report+0xef/0x120 mm/kasan/report.c:516
 kasan_report+0x30/0x60 mm/kasan/common.c:653
 __asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137
 hlist_add_head include/linux/list.h:814 [inline]
 enqueue_timer+0x9e/0x2c0 kernel/time/timer.c:541
 __internal_add_timer kernel/time/timer.c:554 [inline]
 internal_add_timer+0x208/0x3e0 kernel/time/timer.c:604
 __mod_timer+0x5ab/0x1150 kernel/time/timer.c:1065
 mod_timer+0x1f/0x30 kernel/time/timer.c:1117
 tun_flow_init drivers/net/tun.c:1446 [inline]
 tun_net_init+0x2ba/0x580 drivers/net/tun.c:1055
 register_netdevice+0x1c4/0x12a0 net/core/dev.c:9139
 tun_set_iff+0x812/0xe00 drivers/net/tun.c:2922
 __tun_chr_ioctl+0x771/0x18a0 drivers/net/tun.c:3187
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:3470
 do_vfs_ioctl+0x753/0x13f0 fs/ioctl.c:47
 ksys_ioctl fs/ioctl.c:742 [inline]
 __do_sys_ioctl fs/ioctl.c:749 [inline]
 __se_sys_ioctl fs/ioctl.c:747 [inline]
 __x64_sys_ioctl+0xe1/0x120 fs/ioctl.c:747
 do_syscall_64+0xcf/0x170 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
RIP: 0033:0x7f9da41b4969
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9da27fc038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9da43dc080 RCX: 00007f9da41b4969
RDX: 0000200000000200 RSI: 00000000400454ca RDI: 0000000000000007
RBP: 00007f9da4236ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9da43dc080 R15: 00007ffd32961dc8

The buggy address belongs to the page:
page:ffffea0007a188c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8881e31c4d00
flags: 0x8000000000000000()
raw: 8000000000000000 dead000000000100 dead000000000122 0000000000000000
raw: ffff8881e31c4d00 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x102cc2(GFP_HIGHUSER|__GFP_NOWARN)
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2165 [inline]
 prep_new_page+0x35e/0x370 mm/page_alloc.c:2171
 get_page_from_freelist+0x1296/0x1310 mm/page_alloc.c:3794
 __alloc_pages_nodemask+0x202/0x4b0 mm/page_alloc.c:4894
 __alloc_pages include/linux/gfp.h:503 [inline]
 __alloc_pages_node include/linux/gfp.h:516 [inline]
 alloc_pages_node include/linux/gfp.h:530 [inline]
 pcpu_alloc_pages mm/percpu-vm.c:94 [inline]
 pcpu_populate_chunk+0x1b6/0xce0 mm/percpu-vm.c:284
 pcpu_alloc+0x8ec/0x1120 mm/percpu.c:1714
 __alloc_percpu_gfp+0x25/0x30 mm/percpu.c:1783
 prealloc_init+0x24b/0x810 kernel/bpf/hashtab.c:154
 htab_map_alloc+0x65f/0x940 kernel/bpf/hashtab.c:385
 find_and_alloc_map kernel/bpf/syscall.c:122 [inline]
 map_create+0x2d8/0x980 kernel/bpf/syscall.c:573
 __do_sys_bpf kernel/bpf/syscall.c:2873 [inline]
 __se_sys_bpf+0x2dc/0x570 kernel/bpf/syscall.c:2849
 __x64_sys_bpf+0x7b/0x90 kernel/bpf/syscall.c:2849
 do_syscall_64+0xcf/0x170 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1176 [inline]
 __free_pages_ok+0x7e4/0x910 mm/page_alloc.c:1438
 free_the_page mm/page_alloc.c:4956 [inline]
 __free_pages+0x8c/0x110 mm/page_alloc.c:4962
 kfree+0x1ca/0x260 mm/slub.c:4068
 kvfree+0x4c/0x50 mm/util.c:625
 netdev_freemem+0x3f/0x60 net/core/dev.c:9583
 netdev_release+0x7f/0xb0 net/core/net-sysfs.c:1743
 device_release+0x70/0x1a0 drivers/base/core.c:1776
 kobject_cleanup lib/kobject.c:716 [inline]
 kobject_release lib/kobject.c:747 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1fe/0x2c0 lib/kobject.c:764
 put_device+0x1f/0x30 drivers/base/core.c:3010
 free_netdev+0x27e/0x320 net/core/dev.c:9746
 tun_set_iff+0x87c/0xe00 drivers/net/tun.c:2924
 __tun_chr_ioctl+0x771/0x18a0 drivers/net/tun.c:3187
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:3470
 do_vfs_ioctl+0x753/0x13f0 fs/ioctl.c:47
 ksys_ioctl fs/ioctl.c:742 [inline]
 __do_sys_ioctl fs/ioctl.c:749 [inline]
 __se_sys_ioctl fs/ioctl.c:747 [inline]
 __x64_sys_ioctl+0xe1/0x120 fs/ioctl.c:747
 do_syscall_64+0xcf/0x170 arch/x86/entry/common.c:290

Memory state around the buggy address:
 ffff8881e8623080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881e8623100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881e8623180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                                              ^
 ffff8881e8623200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881e8623280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================