CVE-2024-38589
In the Linux kernel, the following vulnerability has been resolved:

netrom: fix possible dead-lock in nr_rt_ioctl()

syzbot loves netrom, and found a possible deadlock in nr_rt_ioctl [1]

Make sure we always acquire nr_node_list_lock before nr_node_lock(nr_node)

[1]
WARNING: possible circular locking dependency detected
6.9.0-rc7-syzkaller-02147-g654de42f3fc6 #0 Not tainted
------------------------------------------------------
syz-executor350/5129 is trying to acquire lock:
 ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
 ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:464 [inline]
 ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1bb/0x1090 net/netrom/nr_route.c:697

but task is already holding lock:
 ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:462 [inline]
 ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x10a/0x1090 net/netrom/nr_route.c:697

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (nr_node_list_lock){+...}-{2:2}:
        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
        __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
        _raw_spin_lock_bh+0x35/0x50 kernel/locking/spinlock.c:178
        spin_lock_bh include/linux/spinlock.h:356 [inline]
        nr_remove_node net/netrom/nr_route.c:299 [inline]
        nr_del_node+0x4b4/0x820 net/netrom/nr_route.c:355
        nr_rt_ioctl+0xa95/0x1090 net/netrom/nr_route.c:683
        sock_do_ioctl+0x158/0x460 net/socket.c:1222
        sock_ioctl+0x629/0x8e0 net/socket.c:1341
        vfs_ioctl fs/ioctl.c:51 [inline]
        __do_sys_ioctl fs/ioctl.c:904 [inline]
        __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:890
        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
        do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&nr_node->node_lock){+...}-{2:2}:
        check_prev_add kernel/locking/lockdep.c:3134 [inline]
        check_prevs_add kernel/locking/lockdep.c:3253 [inline]
        validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
        __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
        __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
        _raw_spin_lock_bh+0x35/0x50 kernel/locking/spinlock.c:178
        spin_lock_bh include/linux/spinlock.h:356 [inline]
        nr_node_lock include/net/netrom.h:152 [inline]
        nr_dec_obs net/netrom/nr_route.c:464 [inline]
        nr_rt_ioctl+0x1bb/0x1090 net/netrom/nr_route.c:697
        sock_do_ioctl+0x158/0x460 net/socket.c:1222
        sock_ioctl+0x629/0x8e0 net/socket.c:1341
        vfs_ioctl fs/ioctl.c:51 [inline]
        __do_sys_ioctl fs/ioctl.c:904 [inline]
        __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:890
        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
        do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor350/5129:
  #0: ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
  #0: ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:462 [inline]
  #0: ffffffff8f70
---truncated---
CVSS v3.1 Score: 5.5 (MEDIUM)
CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Affected Products: linux_kernel
Related CWEs: CWE-667
Related CAPECs: CAPEC-25, CAPEC-27, CAPEC-26
MITRE ATT&CK Techniques: T1499.004
MITRE ATT&CK Tactics: T1499
References: https://git.kernel.org/stable/c/1fbfb483c1a290dce3f41f52d45cc46dd88b7691, https://git.kernel.org/stable/c/3db2fc45d1d2a6457f06ebdfd45b9820e5b5c2b7, https://git.kernel.org/stable/c/421c50fa81836775bf0fd6ce0e57a6eb27af24d5
CWE: CWE-667
MITRE ATT&CK techniques: T1499.004
MITRE ATT&CK tactics: T1499