netlink: 4 bytes leftover after parsing attributes in process `syz.6.4687'. ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 1 PID: 21989 at lib/refcount.c:28 refcount_warn_saturate+0x15a/0x1d0 lib/refcount.c:28 Modules linked in: CPU: 1 UID: 0 PID: 21989 Comm: syz.6.4687 Not tainted 6.12.0-syzkaller-00239-gc6d64479d609 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024 RIP: 0010:refcount_warn_saturate+0x15a/0x1d0 lib/refcount.c:28 Code: 00 01 60 8c e8 17 47 a0 fc 90 0f 0b 90 90 eb 99 e8 2b 58 df fc c6 05 10 63 50 0b 01 90 48 c7 c7 60 01 60 8c e8 f7 46 a0 fc 90 <0f> 0b 90 90 e9 76 ff ff ff e8 08 58 df fc c6 05 ea 62 50 0b 01 90 RSP: 0018:ffffc9000d7a6d70 EFLAGS: 00010246 RAX: 6dc6bb60afa35c00 RBX: ffff88805335f864 RCX: 0000000000040000 RDX: ffffc9001acd8000 RSI: 0000000000004ff3 RDI: 0000000000004ff4 RBP: 0000000000000003 R08: ffffffff8155e222 R09: 1ffffffff2854535 R10: dffffc0000000000 R11: fffffbfff2854536 R12: ffff8880262ab868 R13: ffff88805335f864 R14: 1ffff11004c55718 R15: ffff8880262ab800 FS: 00007f15e6b986c0(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000034374000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: kfree_skb_reason include/linux/skbuff.h:1262 [inline] kfree_skb include/linux/skbuff.h:1271 [inline] j1939_session_destroy net/can/j1939/transport.c:282 [inline] __j1939_session_release net/can/j1939/transport.c:294 [inline] kref_put include/linux/kref.h:65 [inline] j1939_session_put+0x1ed/0x440 net/can/j1939/transport.c:299 j1939_session_deactivate_locked net/can/j1939/transport.c:1086 [inline] j1939_cancel_active_session+0x354/0x490 net/can/j1939/transport.c:2211 j1939_netdev_notify+0xda/0x140 net/can/j1939/main.c:376 notifier_call_chain+0x19f/0x3e0 kernel/notifier.c:93 call_netdevice_notifiers_extack net/core/dev.c:2034 [inline] call_netdevice_notifiers net/core/dev.c:2048 [inline] dev_close_many+0x33c/0x4c0 net/core/dev.c:1589 unregister_netdevice_many_notify+0x530/0x1da0 net/core/dev.c:11381 rtnl_delete_link net/core/rtnetlink.c:3281 [inline] rtnl_dellink+0x50f/0x8e0 net/core/rtnetlink.c:3333 rtnetlink_rcv_msg+0x73f/0xcf0 net/core/rtnetlink.c:6675 netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2541 netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline] netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1347 netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1891 sock_sendmsg_nosec net/socket.c:711 [inline] __sock_sendmsg+0x221/0x270 net/socket.c:726 ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2581 ___sys_sendmsg net/socket.c:2635 [inline] __sys_sendmsg+0x269/0x350 net/socket.c:2667 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f15e5d7e759 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f15e6b98038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f15e5f35f80 RCX: 00007f15e5d7e759 RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000005 RBP: 00007f15e5df175e R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f15e5f35f80 R15: 00007fff930f4048