[syzbot] [net?] KASAN: global-out-of-bounds Read in ip6gre_header

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cf0d9080c6f7 Merge branch 'net-hsr-subsystem-cleanups-and-..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1760a360580000
kernel config: https://syzkaller.appspot.com/x/.config?x=71d49d824b43a0d9
dashboard link: https://syzkaller.appspot.com/bug?extid=d8c285748fa7292580a9
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=11e438d2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=117f19ca580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4271eafdaa2c/disk-cf0d9080.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/984de2c215cb/vmlinux-cf0d9080.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e03ead684811/bzImage-cf0d9080.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d8c285...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in ip6gre_header+0x5bf/0x860 net/ipv6/ip6_gre.c:1400
Read of size 16 at addr ffffffff8c6c4380 by task dhcpcd/5489

CPU: 0 UID: 0 PID: 5489 Comm: dhcpcd 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
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
__asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
ip6gre_header+0x5bf/0x860 net/ipv6/ip6_gre.c:1400
bond_header_create+0x1ce/0x300 drivers/net/bonding/bond_main.c:1524
dev_hard_header include/linux/netdevice.h:3449 [inline]
lapbeth_data_transmit+0x218/0x2e0 drivers/net/wan/lapbether.c:258
lapb_data_transmit+0x90/0xb0 net/lapb/lapb_iface.c:447
lapb_transmit_buffer+0x163/0x200 net/lapb/lapb_out.c:149
lapb_establish_data_link+0x89/0xe0 net/lapb/lapb_out.c:-1
lapb_device_event+0x4e1/0x670 net/lapb/lapb_iface.c:-1
notifier_call_chain+0x1be/0x400 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2285 [inline]
call_netdevice_notifiers net/core/dev.c:2299 [inline]
__dev_notify_flags+0x1a9/0x310 net/core/dev.c:9830
netif_change_flags+0xe8/0x1a0 net/core/dev.c:9859
dev_change_flags+0x130/0x260 net/core/dev_api.c:68
devinet_ioctl+0x9f2/0x1b30 net/ipv4/devinet.c:1199
inet_ioctl+0x42a/0x560 net/ipv4/af_inet.c:1011
sock_do_ioctl+0x101/0x320 net/socket.c:1247
sock_ioctl+0x5c6/0x7f0 net/socket.c:1368
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
RIP: 0033:0x7fb458496378
Code: 00 00 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 10 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 07 89 d0 c3 0f 1f 40 00 48 8b 15 49 3a 0d
RSP: 002b:00007ffdede01158 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000012 RCX: 00007fb458496378
RDX: 00007ffdede11350 RSI: 0000000000008914 RDI: 0000000000000012
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffdede214f0
R13: 00007fb458396708 R14: 0000000000000028 R15: 0000000000008914
</TASK>

The buggy address belongs to the variable:
bcast_addr+0x0/0x20

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xc6c4
flags: 0xfff00000002000(reserved|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000002000 ffffea000031b108 ffffea000031b108 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
ffffffff8c6c4280: 00 00 f9 f9 f9 f9 f9 f9 00 00 00 00 06 f9 f9 f9
ffffffff8c6c4300: f9 f9 f9 f9 00 00 00 00 00 02 f9 f9 f9 f9 f9 f9
>ffffffff8c6c4380: 06 f9 f9 f9 00 00 00 00 00 06 f9 f9 f9 f9 f9 f9
^
ffffffff8c6c4400: 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
ffffffff8c6c4480: 00 05 f9 f9 f9 f9 f9 f9 00 00 00 00 00 06 f9 f9
==================================================================


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