------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 1 PID: 7723 at lib/refcount.c:28 refcount_warn_saturate+0x1c8/0x20c lib/refcount.c:28 Modules linked in: CPU: 1 UID: 0 PID: 7723 Comm: syz.1.219 Not tainted 6.12.0-syzkaller-g7b1d1d4cfac0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : refcount_warn_saturate+0x1c8/0x20c lib/refcount.c:28 lr : refcount_warn_saturate+0x1c8/0x20c lib/refcount.c:28 sp : ffff8000800176f0 x29: ffff8000800176f0 x28: dfff800000000000 x27: ffff0000eed665e4 x26: ffff0000eed66500 x25: 00000000000006f9 x24: 0000000000000000 x23: ffff0000eed665e4 x22: ffff80008a6453b8 x21: 0000000000000003 x20: ffff0000eed665e4 x19: ffff800092b74000 x18: 0000000000000008 x17: 0000000000000000 x16: ffff80008b47f65c x15: ffff700011f29534 x14: 1ffff00011f29534 x13: 0000000000000004 x12: ffffffffffffffff x11: 0000000000000103 x10: 0000000000ff0100 x9 : b049172e18e47100 x8 : b049172e18e47100 x7 : 0000000000000001 x6 : 0000000000000001 x5 : ffff800080016e18 x4 : ffff80008f9bd220 x3 : ffff8000803921b4 x2 : 0000000000000000 x1 : 0000000100000101 x0 : 0000000000000000 Call trace: refcount_warn_saturate+0x1c8/0x20c lib/refcount.c:28 (P) refcount_warn_saturate+0x1c8/0x20c lib/refcount.c:28 (L) __refcount_sub_and_test include/linux/refcount.h:275 [inline] __refcount_dec_and_test include/linux/refcount.h:307 [inline] refcount_dec_and_test include/linux/refcount.h:325 [inline] skb_unref include/linux/skbuff.h:1232 [inline] __sk_skb_reason_drop net/core/skbuff.c:1213 [inline] sk_skb_reason_drop+0x210/0x43c net/core/skbuff.c:1241 kfree_skb_reason include/linux/skbuff.h:1262 [inline] kfree_skb include/linux/skbuff.h:1271 [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+0x464/0xafc net/can/j1939/transport.c:1484 j1939_tp_cmd_recv net/can/j1939/transport.c:2089 [inline] j1939_tp_recv+0x730/0xe14 net/can/j1939/transport.c:2161 j1939_can_recv+0x5bc/0x934 net/can/j1939/main.c:108 deliver net/can/af_can.c:572 [inline] can_rcv_filter+0x308/0x714 net/can/af_can.c:606 can_receive+0x328/0x488 net/can/af_can.c:663 can_rcv+0x128/0x240 net/can/af_can.c:687 __netif_receive_skb_one_core net/core/dev.c:5670 [inline] __netif_receive_skb+0x18c/0x3c8 net/core/dev.c:5783 process_backlog+0x640/0x123c net/core/dev.c:6115 __napi_poll+0xb4/0x3fc net/core/dev.c:6779 napi_poll net/core/dev.c:6848 [inline] net_rx_action+0x6a8/0xf4c net/core/dev.c:6970 handle_softirqs+0x2e0/0xbf8 kernel/softirq.c:554 __do_softirq+0x14/0x20 kernel/softirq.c:588 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:81 call_on_irq_stack+0x24/0x4c arch/arm64/kernel/entry.S:891 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:86 do_softirq+0x90/0xf8 kernel/softirq.c:455 __local_bh_enable_ip+0x288/0x44c kernel/softirq.c:382 local_bh_enable+0x28/0x34 include/linux/bottom_half.h:33 put_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:244 [inline] fpsimd_restore_current_state+0x64/0xec arch/arm64/kernel/fpsimd.c:1811 do_notify_resume+0x114/0x1f4 arch/arm64/kernel/entry-common.c:154 exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:169 [inline] exit_to_user_mode arch/arm64/kernel/entry-common.c:178 [inline] el0_svc+0xac/0x168 arch/arm64/kernel/entry-common.c:745 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600 irq event stamp: 7813 hardirqs last enabled at (7812): [] __up_console_sem kernel/printk/printk.c:344 [inline] hardirqs last enabled at (7812): [] __console_unlock+0x70/0xc4 kernel/printk/printk.c:2844 hardirqs last disabled at (7813): [] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:488 softirqs last enabled at (3264): [] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32 softirqs last disabled at (3265): [] __do_softirq+0x14/0x20 kernel/softirq.c:588 ---[ end trace 0000000000000000 ]--- vcan0: j1939_tp_rxtimer: 0x00000000920e34af: rx timeout, send abort vcan0: j1939_tp_rxtimer: 0x000000009a8ee247: rx timeout, send abort vcan0: j1939_xtp_rx_abort_one: 0x00000000920e34af: 0x00000: (3) A timeout occurred and this is the connection abort to close the session. vcan0: j1939_xtp_rx_abort_one: 0x000000009a8ee247: 0x00000: (3) A timeout occurred and this is the connection abort to close the session.