Re: [syzbot] [net?] WARNING: proc registration bug in atm_dev_register

[Kuniyuki Iwashima <kuni1840@gmail.com>]

From: syzbot <syzbot+8bd335d2ad3b93e80715@syzkaller.appspotmail.com>
Date: Wed, 18 Jun 2025 12:43:26 -0700
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    52da431bf03b Merge tag 'libnvdimm-fixes-6.16-rc3' of git:/..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=17c7de82580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4130f4d8a06c3e71
> dashboard link: https://syzkaller.appspot.com/bug?extid=8bd335d2ad3b93e80715
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=175835d4580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16a7f90c580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/876c709c1090/disk-52da431b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/05dc22ed6dd4/vmlinux-52da431b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/564136f4ae57/bzImage-52da431b.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+8bd335d2ad3b93e80715@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> proc_dir_entry 'atm/atmtcp:0' already registered
> WARNING: CPU: 0 PID: 5919 at fs/proc/generic.c:377 proc_register+0x455/0x5f0 fs/proc/generic.c:377
> Modules linked in:
> CPU: 0 UID: 0 PID: 5919 Comm: syz-executor284 Not tainted 6.16.0-rc2-syzkaller-00047-g52da431bf03b #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:proc_register+0x455/0x5f0 fs/proc/generic.c:377
> Code: 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 a2 01 00 00 48 8b 44 24 10 48 c7 c7 20 c0 c2 8b 48 8b b0 d8 00 00 00 e8 0c 02 1c ff 90 <0f> 0b 90 90 48 c7 c7 80 f2 82 8e e8 0b de 23 09 48 8b 4c 24 28 48
> RSP: 0018:ffffc9000466fa30 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817ae248
> RDX: ffff888026280000 RSI: ffffffff817ae255 RDI: 0000000000000001
> RBP: ffff8880232bed48 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000001 R12: ffff888076ed2140
> R13: dffffc0000000000 R14: ffff888078a61340 R15: ffffed100edda444
> FS:  00007f38b3b0c6c0(0000) GS:ffff888124753000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f38b3bdf953 CR3: 0000000076d58000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  proc_create_data+0xbe/0x110 fs/proc/generic.c:585
>  atm_proc_dev_register+0x112/0x1e0 net/atm/proc.c:361
>  atm_dev_register+0x46d/0x890 net/atm/resources.c:113
>  atmtcp_create+0x77/0x210 drivers/atm/atmtcp.c:369
>  atmtcp_attach drivers/atm/atmtcp.c:403 [inline]
>  atmtcp_ioctl+0x2f9/0xd60 drivers/atm/atmtcp.c:464
>  do_vcc_ioctl+0x12c/0x930 net/atm/ioctl.c:159
>  sock_do_ioctl+0x115/0x280 net/socket.c:1190
>  sock_ioctl+0x227/0x6b0 net/socket.c:1311
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:907 [inline]
>  __se_sys_ioctl fs/ioctl.c:893 [inline]
>  __x64_sys_ioctl+0x18b/0x210 fs/ioctl.c:893
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f38b3b74459
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f38b3b0c198 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f38b3bfe318 RCX: 00007f38b3b74459
> RDX: 0000000000000000 RSI: 0000000000006180 RDI: 0000000000000005
> RBP: 00007f38b3bfe310 R08: 65732f636f72702f R09: 65732f636f72702f
> R10: 65732f636f72702f R11: 0000000000000246 R12: 00007f38b3bcb0ac
> R13: 00007f38b3b0c1a0 R14: 0000200000000200 R15: 00007f38b3bcb03b
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
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> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>

#syz test

diff --git a/net/atm/resources.c b/net/atm/resources.c
index 995d29e7fb13..b19d851e1f44 100644
--- a/net/atm/resources.c
+++ b/net/atm/resources.c
@@ -146,11 +146,10 @@ void atm_dev_deregister(struct atm_dev *dev)
 	 */
 	mutex_lock(&atm_dev_mutex);
 	list_del(&dev->dev_list);
-	mutex_unlock(&atm_dev_mutex);
-
 	atm_dev_release_vccs(dev);
 	atm_unregister_sysfs(dev);
 	atm_proc_dev_deregister(dev);
+	mutex_unlock(&atm_dev_mutex);
 
 	atm_dev_put(dev);
 }