netlink: fix potential deadlock in netlink_set_err()

In the Linux kernel, the following vulnerability has been resolved:

netlink: fix potential deadlock in netlink_set_err()

syzbot reported a possible deadlock in netlink_set_err() [1]

A similar issue was fixed in commit 1d482e666b8e ("netlink: disable IRQs

for netlink_lock_table()") in netlink_lock_table()

This patch adds IRQ safety to netlink_set_err() and __netlink_diag_dump()

which were not covered by cited commit.

[1]

WARNING: possible irq lock inversion dependency detected

6.4.0-rc6-syzkaller-00240-g4e9f0ec38852 #0 Not tainted

syz-executor.2/23011 just changed the state of lock:

ffffffff8e1a7a58 (nl_table_lock){.+.?}-{2:2}, at: netlink_set_err+0x2e/0x3a0 net/netlink/af_netlink.c:1612

but this lock was taken by another, SOFTIRQ-safe lock in the past:

(&local->queue_stop_reason_lock){..-.}-{2:2}

and interrupts could create inverse lock ordering between them.

other info that might help us debug this:

Possible interrupt unsafe locking scenario:

CPU0 CPU1

---- ----

lock(nl_table_lock);

local_irq_disable();

lock(&local->queue_stop_reason_lock);

lock(nl_table_lock);

<Interrupt>

lock(&local->queue_stop_reason_lock);

*** DEADLOCK ***