------------[ cut here ]------------
ida_free called for id=1312 which is not allocated.
WARNING: CPU: 0 PID: 12335 at lib/idr.c:592 ida_free+0x1f9/0x2e0 lib/idr.c:592
Modules linked in:
CPU: 0 UID: 0 PID: 12335 Comm: syz.2.1663 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:ida_free+0x1f9/0x2e0 lib/idr.c:592
Code: 73 f6 41 83 fe 3e 76 72 e8 74 e8 73 f6 48 8b 7c 24 28 4c 89 ee e8 47 39 0d 00 90 48 c7 c7 40 b6 cf 8c 89 ee e8 78 73 32 f6 90 <0f> 0b 90 90 e8 4e e8 73 f6 48 b8 00 00 00 00 00 fc ff df 48 01 c3
RSP: 0018:ffffc90006c57980 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 1ffff92000d8af31 RCX: ffffffff8179b5b8
RDX: ffff88805bbfc900 RSI: ffffffff8179b5c5 RDI: 0000000000000001
RBP: 0000000000000520 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88803225b500
R13: 0000000000000293 R14: 0000000000000120 R15: ffff88803225b520
FS:  0000000000000000(0000) GS:ffff8880d6e55000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f898ad72f98 CR3: 000000005c534000 CR4: 0000000000352ef0
DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 free_mnt_ns+0xe0/0x110 fs/namespace.c:4096
 namespace_unlock+0x542/0x920 fs/namespace.c:1701
 put_mnt_ns fs/namespace.c:6135 [inline]
 put_mnt_ns+0xf5/0x120 fs/namespace.c:6126
 free_nsproxy+0x3a/0x400 kernel/nsproxy.c:188
 put_nsproxy include/linux/nsproxy.h:107 [inline]
 switch_task_namespaces+0xeb/0x100 kernel/nsproxy.c:241
 do_exit+0x86a/0x2bf0 kernel/exit.c:960
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1102
 get_signal+0x2671/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7c0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x7a/0x100 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x419/0x4e0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8989f8eec9
Code: Unable to access opcode bytes at 0x7f8989f8ee9f.
RSP: 002b:00007f898adb5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: fffffffffffffff4 RBX: 00007f898a1e5fa0 RCX: 00007f8989f8eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000002a020480
RBP: 00007f898a011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f898a1e6038 R14: 00007f898a1e5fa0 R15: 00007ffdadc78578
 </TASK>