Message-ID: <685d4c2a.a00a0220.2e5631.028c.GAE@google.com>
Date: Thu, 26 Jun 2025 06:33:30 -0700
From: syzbot <syzbot+14afda08dc3484d5db82@...kaller.appspotmail.com>
To: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, 
	kuba@...nel.org, linux-hams@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [hams?] possible deadlock in nr_rt_ioctl (2)

Hello,

syzbot found the following issue on:

HEAD commit:    09a0fa92e5b4 Merge tag 'selinux-pr-20250107' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=122714b0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7bdfbaac3fbb90d6
dashboard link: https://syzkaller.appspot.com/bug?extid=14afda08dc3484d5db82
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=17b8db0f980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-09a0fa92.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/38215ac79538/vmlinux-09a0fa92.xz
kernel image: https://storage.googleapis.com/syzbot-assets/117da94a1c81/bzImage-09a0fa92.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14afda08dc3484d5db82@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.13.0-rc6-syzkaller-00038-g09a0fa92e5b4 #0 Not tainted
------------------------------------------------------
syz.3.32/6172 is trying to acquire lock:
ffffffff9012a4f8 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff9012a4f8 (nr_neigh_list_lock){+...}-{3:3}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffffffff9012a4f8 (nr_neigh_list_lock){+...}-{3:3}, at: nr_del_node net/netrom/nr_route.c:342 [inline]
ffffffff9012a4f8 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x207f/0x29e0 net/netrom/nr_route.c:678

but task is already holding lock:
ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_del_node net/netrom/nr_route.c:335 [inline]
ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x2aa/0x29e0 net/netrom/nr_route.c:678

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_node_lock include/net/netrom.h:152 [inline]
       nr_rt_device_down+0x188/0x7f0 net/netrom/nr_route.c:519
       nr_device_event+0x126/0x170 net/netrom/af_netrom.c:126
       notifier_call_chain+0xb7/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1996
       call_netdevice_notifiers_extack net/core/dev.c:2034 [inline]
       call_netdevice_notifiers net/core/dev.c:2048 [inline]
       __dev_notify_flags+0x1f9/0x2e0 net/core/dev.c:8992
       dev_change_flags+0x10c/0x160 net/core/dev.c:9028
       dev_ifsioc+0x9c8/0x10b0 net/core/dev_ioctl.c:526
       dev_ioctl+0x224/0x10c0 net/core/dev_ioctl.c:783
       sock_do_ioctl+0x19e/0x280 net/socket.c:1223
       sock_ioctl+0x228/0x6c0 net/socket.c:1328
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_node_list_lock){+...}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xd5/0x7f0 net/netrom/nr_route.c:517
       nr_device_event+0x126/0x170 net/netrom/af_netrom.c:126
       notifier_call_chain+0xb7/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1996
       call_netdevice_notifiers_extack net/core/dev.c:2034 [inline]
       call_netdevice_notifiers net/core/dev.c:2048 [inline]
       __dev_notify_flags+0x1f9/0x2e0 net/core/dev.c:8992
       dev_change_flags+0x10c/0x160 net/core/dev.c:9028
       dev_ifsioc+0x9c8/0x10b0 net/core/dev_ioctl.c:526
       dev_ioctl+0x224/0x10c0 net/core/dev_ioctl.c:783
       sock_do_ioctl+0x19e/0x280 net/socket.c:1223
       sock_ioctl+0x228/0x6c0 net/socket.c:1328
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_neigh_list_lock){+...}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain kernel/locking/lockdep.c:3904 [inline]
       __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
       lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_remove_neigh net/netrom/nr_route.c:307 [inline]
       nr_del_node net/netrom/nr_route.c:342 [inline]
       nr_rt_ioctl+0x207f/0x29e0 net/netrom/nr_route.c:678
       nr_ioctl+0x19a/0x2e0 net/netrom/af_netrom.c:1254
       sock_do_ioctl+0x116/0x280 net/socket.c:1209
       sock_ioctl+0x228/0x6c0 net/socket.c:1328
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  nr_neigh_list_lock --> nr_node_list_lock --> &nr_node->node_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&nr_node->node_lock);
                               lock(nr_node_list_lock);
                               lock(&nr_node->node_lock);
  lock(nr_neigh_list_lock);

 *** DEADLOCK ***

2 locks held by syz.3.32/6172:
 #0: ffffffff9012a558 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffffffff9012a558 (nr_node_list_lock){+...}-{3:3}, at: nr_del_node net/netrom/nr_route.c:334 [inline]
 #0: ffffffff9012a558 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x22e/0x29e0 net/netrom/nr_route.c:678
 #1: ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #1: ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_del_node net/netrom/nr_route.c:335 [inline]
 #1: ffff88810370fa70 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x2aa/0x29e0 net/netrom/nr_route.c:678

stack backtrace:
CPU: 3 UID: 0 PID: 6172 Comm: syz.3.32 Not tainted 6.13.0-rc6-syzkaller-00038-g09a0fa92e5b4 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x419/0x5d0 kernel/locking/lockdep.c:2074
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain kernel/locking/lockdep.c:3904 [inline]
 __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 nr_remove_neigh net/netrom/nr_route.c:307 [inline]
 nr_del_node net/netrom/nr_route.c:342 [inline]
 nr_rt_ioctl+0x207f/0x29e0 net/netrom/nr_route.c:678
 nr_ioctl+0x19a/0x2e0 net/netrom/af_netrom.c:1254
 sock_do_ioctl+0x116/0x280 net/socket.c:1209
 sock_ioctl+0x228/0x6c0 net/socket.c:1328
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl fs/ioctl.c:892 [inline]
 __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbff7985d29
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:00007fbff8769038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbff7b75fa0 RCX: 00007fbff7985d29
RDX: 0000000020000180 RSI: 000000000000890c RDI: 0000000000000005
RBP: 00007fbff7a01b08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fbff7b75fa0 R15: 00007ffd23708838
 </TASK>


---
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