lockdown: ratelimit denial messages

User space can flood the log with lockdown denial messages:

[ 662.555584] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7
[ 662.563237] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7
[ 662.571134] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7
[ 662.578668] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7
[ 662.586021] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7
[ 662.593398] Lockdown: bash: debugfs access is restricted; see man kernel_lockdown.7

Ratelimiting these shouldn't meaningfully degrade the quality of the
information logged.

Signed-off-by: Nathan Lynch <[e-mail]>
Signed-off-by: Paul Moore <[e-mail]>

security/lockdown/lockdown.c

···
 
 	if (kernel_locked_down >= what) {
 		if (lockdown_reasons[what])
-			pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
+			pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
 				  current->comm, lockdown_reasons[what]);
 		return -EPERM;
 	}