Subject: [syzbot] [can?] WARNING: refcount bug in j1939_xtp_rx_cts

From: syzbot <[email-masked]>
Date: Mon, 05 Aug 2024 14:29:36 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    743ff02152bc ethtool: Don't check for NULL info in prepare..
git tree:       net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1058b26d980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5efb917b1462a973
dashboard link: https://syzkaller.appspot.com/bug?extid=5a1281566cc25c9881e0
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15041155980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162bd19d980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/69cb8d5cd046/disk-743ff021.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8f52c95a23c5/vmlinux-743ff021.xz
kernel image: https://storage.googleapis.com/syzbot-assets/93f2f40e650b/bzImage-743ff021.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 8 at lib/refcount.c:28 refcount_warn_saturate+0x15a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 0 UID: 0 PID: 8 Comm: kworker/0:0 Not tainted 6.10.0-syzkaller-12610-g743ff02152bc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Workqueue: events nsim_dev_trap_report_work
RIP: 0010:refcount_warn_saturate+0x15a/0x1d0 lib/refcount.c:28
Code: 00 17 40 8c e8 67 97 a5 fc 90 0f 0b 90 90 eb 99 e8 1b 89 e3 fc c6 05 76 7d 31 0b 01 90 48 c7 c7 60 17 40 8c e8 47 97 a5 fc 90 <0f> 0b 90 90 e9 76 ff ff ff e8 f8 88 e3 fc c6 05 50 7d 31 0b 01 90
RSP: 0018:ffffc900000076e0 EFLAGS: 00010246
RAX: b72359b2da0c4a00 RBX: ffff8880213d1864 RCX: ffff8880176cda00
RDX: 0000000080000102 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000003 R08: ffffffff81559432 R09: 1ffff1101724519a
R10: dffffc0000000000 R11: ffffed101724519b R12: ffff88802b3dac00
R13: ffff8880213d1864 R14: ffff88802b3dac00 R15: ffff888077daa118
FS:  0000000000000000(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005626f04f7000 CR3: 000000007c7d2000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 kfree_skb_reason include/linux/skbuff.h:1260 [inline]
 kfree_skb include/linux/skbuff.h:1269 [inline]
 j1939_session_skb_drop_old net/can/j1939/transport.c:347 [inline]
 j1939_xtp_rx_cts_one net/can/j1939/transport.c:1445 [inline]
 j1939_xtp_rx_cts+0x54f/0xc70 net/can/j1939/transport.c:1484
 j1939_tp_cmd_recv net/can/j1939/transport.c:2089 [inline]
 j1939_tp_recv+0x8ae/0x1050 net/can/j1939/transport.c:2161
 j1939_can_recv+0x732/0xb20 net/can/j1939/main.c:108
 deliver net/can/af_can.c:572 [inline]
 can_rcv_filter+0x359/0x7f0 net/can/af_can.c:606
 can_receive+0x31c/0x470 net/can/af_can.c:663
 can_rcv+0x144/0x260 net/can/af_can.c:687
 __netif_receive_skb_one_core net/core/dev.c:5660 [inline]
 __netif_receive_skb+0x2e0/0x650 net/core/dev.c:5774
 process_backlog+0x662/0x15b0 net/core/dev.c:6107
 __napi_poll+0xcb/0x490 net/core/dev.c:6771
 napi_poll net/core/dev.c:6840 [inline]
 net_rx_action+0x89b/0x1240 net/core/dev.c:6962
 handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
 do_softirq+0x11b/0x1e0 kernel/softirq.c:455
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x1bb/0x200 kernel/softirq.c:382
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:820 [inline]
 nsim_dev_trap_report_work+0x75d/0xaa0 drivers/net/netdevsim/dev.c:850
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
 worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

---
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