netlink: 4 bytes leftover after parsing attributes in process `syz.1.208'. ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 3 PID: 6233 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28 Modules linked in: CPU: 3 UID: 0 PID: 6233 Comm: syz.1.208 Not tainted 6.12.0-rc1-syzkaller-00306-g27cc6fdf7201 #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28 Code: ff 89 de e8 a8 2e 04 fd 84 db 0f 85 66 ff ff ff e8 bb 2c 04 fd c6 05 0a 14 7d 0b 01 90 48 c7 c7 60 d6 b0 8b e8 07 ac c5 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 98 2c 04 fd 0f b6 1d e5 13 7d 0b 31 RSP: 0018:ffffc9000324ee50 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc90034861000 RDX: 0000000000040000 RSI: ffffffff814e28c6 RDI: 0000000000000001 RBP: ffff88800041bee4 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002 R13: 0000000000000000 R14: ffff88800041bee4 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff88802b700000(0063) knlGS:00000000f5776b40 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 00007f0084dc049f CR3: 00000000776de000 CR4: 0000000000352ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __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+0x183/0x1a0 net/core/skbuff.c:1241 kfree_skb_reason include/linux/skbuff.h:1262 [inline] kfree_skb include/linux/skbuff.h:1271 [inline] j1939_session_destroy+0x163/0x460 net/can/j1939/transport.c:282 __j1939_session_release net/can/j1939/transport.c:294 [inline] kref_put include/linux/kref.h:65 [inline] j1939_session_put net/can/j1939/transport.c:299 [inline] j1939_session_deactivate_locked+0x275/0x320 net/can/j1939/transport.c:1086 j1939_cancel_active_session+0x183/0x350 net/can/j1939/transport.c:2211 j1939_netdev_notify+0x19e/0x1e0 net/can/j1939/main.c:376 notifier_call_chain+0xb9/0x410 kernel/notifier.c:93 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1996 call_netdevice_notifiers_extack net/core/dev.c:2034 [inline] call_netdevice_notifiers net/core/dev.c:2048 [inline] dev_close_many+0x333/0x6a0 net/core/dev.c:1589 unregister_netdevice_many_notify+0x489/0x1e50 net/core/dev.c:11377 rtnl_delete_link net/core/rtnetlink.c:3252 [inline] rtnl_dellink+0x3c9/0xae0 net/core/rtnetlink.c:3304 rtnetlink_rcv_msg+0x3c7/0xea0 net/core/rtnetlink.c:6646 netlink_rcv_skb+0x165/0x410 net/netlink/af_netlink.c:2550 netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline] netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1357 netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1901 sock_sendmsg_nosec net/socket.c:729 [inline] __sock_sendmsg net/socket.c:744 [inline] ____sys_sendmsg+0x9ae/0xb40 net/socket.c:2602 ___sys_sendmsg+0x135/0x1e0 net/socket.c:2656 __sys_sendmsg+0x117/0x1f0 net/socket.c:2685 do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline] __do_fast_syscall_32+0x73/0x120 arch/x86/entry/common.c:386 do_fast_syscall_32+0x32/0x80 arch/x86/entry/common.c:411 entry_SYSENTER_compat_after_hwframe+0x84/0x8e RIP: 0023:0xf7ff6579 Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00 RSP: 002b:00000000f577656c EFLAGS: 00000296 ORIG_RAX: 0000000000000172 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020000200 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 ---------------- Code disassembly (best guess), 2 bytes skipped: 0: 10 06 adc %al,(%rsi) 2: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi 6: 10 07 adc %al,(%rdi) 8: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi c: 10 08 adc %cl,(%rax) e: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi 1e: 00 51 52 add %dl,0x52(%rcx) 21: 55 push %rbp 22: 89 e5 mov %esp,%ebp 24: 0f 34 sysenter 26: cd 80 int $0x80 * 28: 5d pop %rbp <-- trapping instruction 29: 5a pop %rdx 2a: 59 pop %rcx 2b: c3 ret 2c: 90 nop 2d: 90 nop 2e: 90 nop 2f: 90 nop 30: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi 37: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi