------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 5988 at lib/refcount.c:28 refcount_warn_saturate+0x15a/0x1d0 lib/refcount.c:28 Modules linked in: CPU: 0 UID: 0 PID: 5988 Comm: syz.0.13 Not tainted 6.12.0-rc7-syzkaller-01770-gdd7207838d38 #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: e0 c8 60 8c e8 d7 13 98 fc 90 0f 0b 90 90 eb 99 e8 5b 1d d7 fc c6 05 7d 6b 49 0b 01 90 48 c7 c7 40 c9 60 8c e8 b7 13 98 fc 90 <0f> 0b 90 90 e9 76 ff ff ff e8 38 1d d7 fc c6 05 57 6b 49 0b 01 90 RSP: 0018:ffffc9000439f908 EFLAGS: 00010246 RAX: e689f44e4ca3d000 RBX: ffff88807c5bc724 RCX: 0000000000080000 RDX: ffffc9000bac9000 RSI: 00000000000031e1 RDI: 00000000000031e2 RBP: 0000000000000003 R08: ffffffff8155e312 R09: fffffbfff1cf9fd0 R10: dffffc0000000000 R11: fffffbfff1cf9fd0 R12: ffff88807b821468 R13: ffff88807c5bc724 R14: 1ffff1100f704298 R15: ffff88807b821400 FS: 00007f9505fe96c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b31618ff8 CR3: 000000002a16c000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: kfree_skb_reason include/linux/skbuff.h:1263 [inline] kfree_skb include/linux/skbuff.h:1272 [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_sk_send_loop net/can/j1939/socket.c:1202 [inline] j1939_sk_sendmsg+0x121b/0x14c0 net/can/j1939/socket.c:1277 sock_sendmsg_nosec net/socket.c:729 [inline] __sock_sendmsg+0x221/0x270 net/socket.c:744 ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2609 ___sys_sendmsg net/socket.c:2663 [inline] __sys_sendmsg+0x292/0x380 net/socket.c:2692 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: 0033:0x7f950517e819 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:00007f9505fe9038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f9505335fa0 RCX: 00007f950517e819 RDX: 0000000000000000 RSI: 00000000200002c0 RDI: 0000000000000008 RBP: 00007f95051f175e R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f9505335fa0 R15: 00007fff4aa528b8