------------[ cut here ]------------
ida_free called for id=1381 which is not allocated.
WARNING: CPU: 0 PID: 6462 at lib/idr.c:592 ida_free+0x280/0x310 lib/idr.c:592
Modules linked in:
CPU: 0 UID: 0 PID: 6462 Comm: syz.1.268 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+0x280/0x310 lib/idr.c:592
Code: 00 00 00 00 fc ff df 48 8b 5c 24 10 48 8b 7c 24 40 48 89 de e8 d1 8a 0c 00 90 48 c7 c7 20 1b db 8c 44 89 fe e8 11 f7 0f f6 90 <0f> 0b 90 90 eb 34 e8 a5 7c 4c f6 49 bd 00 00 00 00 00 fc ff df eb
RSP: 0018:ffffc9000e67fae0 EFLAGS: 00010246
RAX: 41756ac06cc25e00 RBX: 0000000000000a06 RCX: ffff88803136a440
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc9000e67fbc8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1c3a23c R12: 1ffff92001ccff60
R13: dffffc0000000000 R14: ffff888041ee2a00 R15: 0000000000000565
FS:  00007f00bd5886c0(0000) GS:ffff88808d001000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff36d2aee8 CR3: 0000000059229000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 free_mnt_ns+0x52/0xe0 fs/namespace.c:4096
 namespace_unlock+0x529/0x760 fs/namespace.c:1701
 create_new_namespaces+0x637/0x720 kernel/nsproxy.c:137
 unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:218
 ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3127
 __do_sys_unshare kernel/fork.c:3198 [inline]
 __se_sys_unshare kernel/fork.c:3196 [inline]
 __x64_sys_unshare+0x38/0x50 kernel/fork.c:3196
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f00bc78eec9
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:00007f00bd588038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f00bc9e5fa0 RCX: 00007f00bc78eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000002a060400
RBP: 00007f00bc811f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f00bc9e6038 R14: 00007f00bc9e5fa0 R15: 00007fffc3771578
 </TASK>