[syzbot] [net?] KASAN: null-ptr-deref Write in send_to_lecd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 014441d1e4b2 Merge tag 'i2c-for-7.0-rc3' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11230d52580000
kernel config: https://syzkaller.appspot.com/x/.config?x=976ba5a93c4add9e
dashboard link: https://syzkaller.appspot.com/bug?extid=e1d2b89a60c8bb9a7f33
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c6996386f74c/disk-014441d1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/50d7e742ec37/vmlinux-014441d1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8b042e15289c/bzImage-014441d1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e1d2b8...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: null-ptr-deref in atomic_add include/linux/atomic/atomic-instrumented.h:104 [inline]
BUG: KASAN: null-ptr-deref in atm_force_charge include/linux/atmdev.h:261 [inline]
BUG: KASAN: null-ptr-deref in send_to_lecd+0x2ef/0x5e0 net/atm/lec.c:535
Write of size 4 at addr 0000000000000140 by task dhcpcd/28797

CPU: 1 UID: 101 PID: 28797 Comm: dhcpcd Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
kasan_report+0xdf/0x1e0 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:186 [inline]
kasan_check_range+0x10f/0x1e0 mm/kasan/generic.c:200
instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
atomic_add include/linux/atomic/atomic-instrumented.h:104 [inline]
atm_force_charge include/linux/atmdev.h:261 [inline]
send_to_lecd+0x2ef/0x5e0 net/atm/lec.c:535
lec_arp_resolve net/atm/lec.c:1791 [inline]
lec_start_xmit+0x1252/0x2070 net/atm/lec.c:285
__netdev_start_xmit include/linux/netdevice.h:5292 [inline]
netdev_start_xmit include/linux/netdevice.h:5301 [inline]
xmit_one net/core/dev.c:3871 [inline]
dev_hard_start_xmit+0x121/0x7d0 net/core/dev.c:3887
sch_direct_xmit+0x1b2/0xc60 net/sched/sch_generic.c:347
qdisc_restart net/sched/sch_generic.c:412 [inline]
__qdisc_run+0x52d/0x1b10 net/sched/sch_generic.c:420
qdisc_run include/net/pkt_sched.h:120 [inline]
qdisc_run include/net/pkt_sched.h:117 [inline]
__dev_xmit_skb net/core/dev.c:4196 [inline]
__dev_queue_xmit+0x196d/0x4800 net/core/dev.c:4802
dev_queue_xmit include/linux/netdevice.h:3384 [inline]
packet_xmit+0x243/0x310 net/packet/af_packet.c:275
packet_snd net/packet/af_packet.c:3076 [inline]
packet_sendmsg+0x32f4/0x53c0 net/packet/af_packet.c:3108
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
sock_write_iter+0x524/0x5a0 net/socket.c:1195
do_iter_readv_writev+0x6ee/0x920 fs/read_write.c:829
vfs_writev+0x360/0xe10 fs/read_write.c:1059
do_writev+0x28a/0x340 fs/read_write.c:1105
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f53f6e3c407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007fff9cf80170 EFLAGS: 00000202 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f53f6db2780 RCX: 00007f53f6e3c407
RDX: 0000000000000002 RSI: 00007fff9cf801d0 RDI: 0000000000000003
RBP: 0000000000000188 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff9cf80210
R13: 0000562512791790 R14: 00007fff9cf80260 R15: 00007fff9cf90430
</TASK>
==================================================================


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