[syzbot ci] Re: pidfs: add inode ownership and permission checks

[syzbot ci <syzbot+cieda7985262b19968@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] pidfs: add inode ownership and permission checks
https://lore.kernel.org/all/20260216-work-pidfs-inode-owner-v1-1-f8faa6b73983@kernel.org
* [PATCH RFC] pidfs: add inode ownership and permission checks

and found the following issue:
general protection fault in pidfs_fill_owner

Full report is available here:
https://ci.syzbot.org/series/d1c7b2f5-ccdc-4ca8-af27-dd6c97fd9e90

***

general protection fault in pidfs_fill_owner

tree:      bpf-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/bpf/bpf-next.git
base:      72c395024dac5e215136cbff793455f065603b06
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/a2c9422a-a065-455a-83e1-f304e9567e3e/config
syz repro: https://ci.syzbot.org/findings/b2100115-a69c-42ec-8aa0-29353ad7bd45/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 0 UID: 0 PID: 5803 Comm: syz-execprog Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:pidfs_fill_owner+0x1f5/0x500 fs/pidfs.c:743
Code: ff 49 83 c4 20 4c 89 e0 48 c1 e8 03 42 80 3c 30 00 74 08 4c 89 e7 e8 3a f2 da ff 4d 8b 2c 24 49 83 c5 18 4c 89 e8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 7b 02 00 00 41 8b 6d 00 4c 89 f8 48 c1
RSP: 0018:ffffc90004997850 EFLAGS: 00010206
RAX: 0000000000000003 RBX: ffffffff8251bdfe RCX: ffff888175390000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffffff8251bdfe R09: ffffffff8e558220
R10: dffffc0000000000 R11: fffffbfff1fdf4ef R12: ffff8881078adaa0
R13: 0000000000000018 R14: dffffc0000000000 R15: ffff8881169793f8
FS:  000000c00007a898(0000) GS:ffff88818e0d7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c002961200 CR3: 000000016d248000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 pidfs_update_inode fs/pidfs.c:766 [inline]
 pidfs_stash_dentry+0xf2/0x280 fs/pidfs.c:1073
 path_from_stashed+0x463/0x5c0 fs/libfs.c:2258
 pidfs_alloc_file+0xff/0x290 fs/pidfs.c:1182
 pidfd_prepare+0x14e/0x1b0 kernel/fork.c:1898
 copy_process+0x1f3a/0x3cf0 kernel/fork.c:2259
 kernel_clone+0x248/0x870 kernel/fork.c:2654
 __do_sys_clone kernel/fork.c:2795 [inline]
 __se_sys_clone kernel/fork.c:2779 [inline]
 __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2779
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x4a7d4d
Code: 24 10 48 8b 74 24 18 48 8b 54 24 20 49 c7 c2 00 00 00 00 49 c7 c0 00 00 00 00 49 c7 c1 00 00 00 00 48 8b 44 24 08 41 5c 0f 05 <41> 54 48 3d 01 f0 ff ff 76 12 48 c7 44 24 28 ff ff ff ff 48 f7 d8
RSP: 002b:000000c00001d5b8 EFLAGS: 00000216 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004a7d4d
RDX: 000000c00001d644 RSI: 0000000000000000 RDI: 0000000000005100
RBP: 000000c00001d5f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 000000000049fd97
R13: 0000000000000000 R14: 000000c000002380 R15: 000000c000010020
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:pidfs_fill_owner+0x1f5/0x500 fs/pidfs.c:743
Code: ff 49 83 c4 20 4c 89 e0 48 c1 e8 03 42 80 3c 30 00 74 08 4c 89 e7 e8 3a f2 da ff 4d 8b 2c 24 49 83 c5 18 4c 89 e8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 7b 02 00 00 41 8b 6d 00 4c 89 f8 48 c1
RSP: 0018:ffffc90004997850 EFLAGS: 00010206
RAX: 0000000000000003 RBX: ffffffff8251bdfe RCX: ffff888175390000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffffff8251bdfe R09: ffffffff8e558220
R10: dffffc0000000000 R11: fffffbfff1fdf4ef R12: ffff8881078adaa0
R13: 0000000000000018 R14: dffffc0000000000 R15: ffff8881169793f8
FS:  000000c00007a898(0000) GS:ffff88818e0d7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c002961200 CR3: 000000016d248000 CR4: 00000000000006f0
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	49 83 c4 20          	add    $0x20,%r12
   4:	4c 89 e0             	mov    %r12,%rax
   7:	48 c1 e8 03          	shr    $0x3,%rax
   b:	42 80 3c 30 00       	cmpb   $0x0,(%rax,%r14,1)
  10:	74 08                	je     0x1a
  12:	4c 89 e7             	mov    %r12,%rdi
  15:	e8 3a f2 da ff       	call   0xffdaf254
  1a:	4d 8b 2c 24          	mov    (%r12),%r13
  1e:	49 83 c5 18          	add    $0x18,%r13
  22:	4c 89 e8             	mov    %r13,%rax
  25:	48 c1 e8 03          	shr    $0x3,%rax
* 29:	42 0f b6 04 30       	movzbl (%rax,%r14,1),%eax <-- trapping instruction
  2e:	84 c0                	test   %al,%al
  30:	0f 85 7b 02 00 00    	jne    0x2b1
  36:	41 8b 6d 00          	mov    0x0(%r13),%ebp
  3a:	4c 89 f8             	mov    %r15,%rax
  3d:	48                   	rex.W
  3e:	c1                   	.byte 0xc1


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

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