[v5.15] KASAN: global-out-of-bounds Read in drop_sysctl_table

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 91d48252ad4b Linux 5.15.202
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=104d8102580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=005769f5851f618e7b41
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/74e75dfcb812/disk-91d48252.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bfa72aab00f2/vmlinux-91d48252.xz
kernel image: https://storage.googleapis.com/syzbot-assets/47ea72d1c7dc/bzImage-91d48252.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+005769...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in drop_sysctl_table+0xa7/0x4e0 fs/proc/proc_sysctl.c:1674
Read of size 8 at addr ffffffff9669efd8 by task syz.2.861/7421

CPU: 0 PID: 7421 Comm: syz.2.861 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
print_address_description+0x60/0x2d0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0xdf/0x130 mm/kasan/report.c:451
drop_sysctl_table+0xa7/0x4e0 fs/proc/proc_sysctl.c:1674
unregister_sysctl_table+0x87/0x130 fs/proc/proc_sysctl.c:1723
ax25_unregister_dev_sysctl+0x79/0xa0 net/ax25/sysctl_net_ax25.c:178
ax25_dev_device_down+0x5b/0x520 net/ax25/ax25_dev.c:101
ax25_device_event+0x4b4/0x4f0 net/ax25/af_ax25.c:144
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
call_netdevice_notifiers_extack net/core/dev.c:2074 [inline]
call_netdevice_notifiers net/core/dev.c:2088 [inline]
__dev_notify_flags+0x158/0x300 net/core/dev.c:8919
dev_change_flags+0xe3/0x1a0 net/core/dev.c:8955
dev_ifsioc+0x130/0xd50 net/core/dev_ioctl.c:324
dev_ioctl+0x545/0xe30 net/core/dev_ioctl.c:572
sock_do_ioctl+0x245/0x320 net/socket.c:1161
sock_ioctl+0x4d2/0x710 net/socket.c:1266
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f2fb847e799
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:00007f2fb66b7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f2fb86f8090 RCX: 00007f2fb847e799
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 0000000000000006
RBP: 00007f2fb8514c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2fb86f8128 R14: 00007f2fb86f8090 R15: 00007ffc89ad4c78
</TASK>

The buggy address belongs to the variable:
instance_create.__key+0x18/0x20

Memory state around the buggy address:
ffffffff9669ee80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffffff9669ef00: 00 00 00 00 00 00 00 00 00 00 f9 f9 f9 f9 f9 f9
>ffffffff9669ef80: 00 00 f9 f9 00 00 f9 f9 00 00 f9 f9 00 00 f9 f9
^
ffffffff9669f000: 00 00 f9 f9 00 00 00 00 f9 f9 f9 f9 01 f9 f9 f9
ffffffff9669f080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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