Re: [syzbot] [kernel?] general protection fault in put_pid_ns

[syzbot <syzbot+983e44006c89c92789a4@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in put_pid_ns

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000017: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000000b8-0x00000000000000bf]
CPU: 1 UID: 0 PID: 6441 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:is_ns_init_id include/linux/ns_common.h:25 [inline]
RIP: 0010:__ns_ref_put include/linux/ns_common.h:70 [inline]
RIP: 0010:put_pid_ns+0x37/0x2a0 kernel/pid_namespace.c:187
Code: 53 48 89 fb e8 6a ba 03 00 48 85 db 0f 84 e8 00 00 00 49 bc 00 00 00 00 00 fc ff df 4c 8d b3 d0 00 00 00 4d 89 f5 49 c1 ed 03 <43> 80 7c 25 00 00 74 08 4c 89 f7 e8 d9 76 69 00 4d 8b 3e 31 ff 4c
RSP: 0018:ffffc90002e67cd0 EFLAGS: 00010206
RAX: ffffffff81bcf846 RBX: ffffffffffffffea RCX: ffff888026439e40
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffffffffea
RBP: 0000000000000002 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005ccf78 R12: dffffc0000000000
R13: 0000000000000017 R14: 00000000000000ba R15: ffff888076ba2c5c
FS:  00007f9ac4b9c6c0(0000) GS:ffff888125df1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2f863fff CR3: 0000000032c7e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nsproxy_free+0x20f/0x7c0 kernel/nsproxy.c:68
 __free_nsproxy_free kernel/nsproxy.c:76 [inline]
 create_new_namespaces+0x47a/0x540 kernel/nsproxy.c:132
 unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:197
 ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3130
 __do_sys_unshare kernel/fork.c:3201 [inline]
 __se_sys_unshare kernel/fork.c:3199 [inline]
 __x64_sys_unshare+0x38/0x50 kernel/fork.c:3199
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9ac3d8f6c9
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:00007f9ac4b9c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f9ac3fe5fa0 RCX: 00007f9ac3d8f6c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000022020400
RBP: 00007f9ac3e11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9ac3fe6038 R14: 00007f9ac3fe5fa0 R15: 00007ffc1a2a21f8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:is_ns_init_id include/linux/ns_common.h:25 [inline]
RIP: 0010:__ns_ref_put include/linux/ns_common.h:70 [inline]
RIP: 0010:put_pid_ns+0x37/0x2a0 kernel/pid_namespace.c:187
Code: 53 48 89 fb e8 6a ba 03 00 48 85 db 0f 84 e8 00 00 00 49 bc 00 00 00 00 00 fc ff df 4c 8d b3 d0 00 00 00 4d 89 f5 49 c1 ed 03 <43> 80 7c 25 00 00 74 08 4c 89 f7 e8 d9 76 69 00 4d 8b 3e 31 ff 4c
RSP: 0018:ffffc90002e67cd0 EFLAGS: 00010206
RAX: ffffffff81bcf846 RBX: ffffffffffffffea RCX: ffff888026439e40
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffffffffea
RBP: 0000000000000002 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005ccf78 R12: dffffc0000000000
R13: 0000000000000017 R14: 00000000000000ba R15: ffff888076ba2c5c
FS:  00007f9ac4b9c6c0(0000) GS:ffff888125cf1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005556396ca000 CR3: 0000000032c7e000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	53                   	push   %rbx
   1:	48 89 fb             	mov    %rdi,%rbx
   4:	e8 6a ba 03 00       	call   0x3ba73
   9:	48 85 db             	test   %rbx,%rbx
   c:	0f 84 e8 00 00 00    	je     0xfa
  12:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  19:	fc ff df
  1c:	4c 8d b3 d0 00 00 00 	lea    0xd0(%rbx),%r14
  23:	4d 89 f5             	mov    %r14,%r13
  26:	49 c1 ed 03          	shr    $0x3,%r13
* 2a:	43 80 7c 25 00 00    	cmpb   $0x0,0x0(%r13,%r12,1) <-- trapping instruction
  30:	74 08                	je     0x3a
  32:	4c 89 f7             	mov    %r14,%rdi
  35:	e8 d9 76 69 00       	call   0x697713
  3a:	4d 8b 3e             	mov    (%r14),%r15
  3d:	31 ff                	xor    %edi,%edi
  3f:	4c                   	rex.WR


Tested on:

commit:         53974b87 nsproxy: fix free_nsproxy() and simplify crea..
git tree:       https://github.com/brauner/linux.git namespace-6.19
console output: https://syzkaller.appspot.com/x/log.txt?x=1054b532580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1e17ff55912ea78d
dashboard link: https://syzkaller.appspot.com/bug?extid=983e44006c89c92789a4
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.