[syzbot] [kernel?] WARNING in free_uts_ns

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50c19e20ed2e Merge tag 'nolibc-20250928-for-6.18-1' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=157b5d04580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c22ef41a8c536eeb
dashboard link: https://syzkaller.appspot.com/bug?extid=c897acc98cdcbd154885
compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/685748d5e5b4/disk-50c19e20.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8d68642bc16e/vmlinux-50c19e20.xz
kernel image: https://storage.googleapis.com/syzbot-assets/236e2110bcde/bzImage-50c19e20.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c897ac...@syzkaller.appspotmail.com

------------[ cut here ]------------
ida_free called for id=1110 which is not allocated.
WARNING: CPU: 0 PID: 14455 at lib/idr.c:592 ida_free+0x1f9/0x2e0 lib/idr.c:592
Modules linked in:
CPU: 0 UID: 0 PID: 14455 Comm: syz.5.1832 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:ida_free+0x1f9/0x2e0 lib/idr.c:592
Code: 75 f6 41 83 fe 3e 76 72 e8 44 5b 75 f6 48 8b 7c 24 28 4c 89 ee e8 47 39 0d 00 90 48 c7 c7 e0 cb cf 8c 89 ee e8 38 e6 33 f6 90 <0f> 0b 90 90 e8 1e 5b 75 f6 48 b8 00 00 00 00 00 fc ff df 48 01 c3
RSP: 0018:ffffc9000497fa78 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 1ffff9200092ff50 RCX: ffffffff8179a5b8
RDX: ffff88806e472480 RSI: ffffffff8179a5c5 RDI: 0000000000000001
RBP: 0000000000000456 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: fffffffffffe1a68 R12: ffff888027a2a000
R13: 0000000000000293 R14: 0000000000000056 R15: ffff888027a2a008
FS: 0000000000000000(0000) GS:ffff888124e71000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f125e818d58 CR3: 0000000027bfa000 CR4: 00000000003526f0
DR0: 0000000000000002 DR1: 000000000000af51 DR2: 0000000000000800
DR3: 000000007fffffff DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
free_uts_ns+0xe7/0x150 kernel/utsname.c:101
put_uts_ns include/linux/uts_namespace.h:38 [inline]
free_nsproxy+0x32e/0x400 kernel/nsproxy.c:189
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: 0033:0x7f125d98eec9
Code: Unable to access opcode bytes at 0x7f125d98ee9f.
RSP: 002b:00007f125e839038 EFLAGS: 00000246 ORIG_RAX: 0000000000000013
RAX: fffffffffffffe00 RBX: 00007f125dbe5fa0 RCX: 00007f125d98eec9
RDX: 0000000000000001 RSI: 0000200000000100 RDI: 0000000000000006
RBP: 00007f125da11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f125dbe6038 R14: 00007f125dbe5fa0 R15: 00007ffd01722128
</TASK>


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