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---

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-38589
• https://git.kernel.org/stable/c/1fbfb483c1a290dce3f41f52d45cc46dd88b7691
• https://git.kernel.org/stable/c/3db2fc45d1d2a6457f06ebdfd45b9820e5b5c2b7
• https://git.kernel.org/stable/c/421c50fa81836775bf0fd6ce0e57a6eb27af24d5
• https://git.kernel.org/stable/c/5bc50a705cfac8f64ce51c95611c3dd0554ef9c3
• https://git.kernel.org/stable/c/5fb7e2a4335fc67d6952ad2a6613c46e0b05f7c5
• https://git.kernel.org/stable/c/b117e5b4f27c2c9076561b6be450a9619f0b79de
• https://git.kernel.org/stable/c/b9d663fbf74290cb68fbc66ae4367bd56837ad1d
• https://git.kernel.org/stable/c/e03e7f20ebf7e1611d40d1fdc1bde900fd3335f6
• https://git.kernel.org/stable/c/f28bdc2ee5d9300cc77bd3d97b5b3cdd14960fd8
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html