panic: Introduce warn_limit

commit 9fc9e278a5 upstream.

Like oops_limit, add warn_limit for limiting the number of warnings when
panic_on_warn is not set.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: tangmeng <tangmeng@uniontech.com>
Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20221117234328.594699-5-keescook@chromium.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/sysctl/kernel.txt

@@ -94,6 +94,7 @@ show up in /proc/sys/kernel:
 - threads-max
 - unprivileged_bpf_disabled
 - unknown_nmi_panic
+- warn_limit
 - watchdog
 - watchdog_thresh
 - version
@@ -1072,6 +1073,15 @@ example.  If a system hangs up, try pressing the NMI switch.
 
 ==============================================================
 
+warn_limit:
+
+Number of kernel warnings after which the kernel should panic when
+``panic_on_warn`` is not set. Setting this to 0 disables checking
+the warning count. Setting this to 1 has the same effect as setting
+``panic_on_warn=1``. The default value is 0.
+
+==============================================================
+
 watchdog:
 
 This parameter can be used to disable or enable the soft lockup detector

kernel/panic.c

@@ -39,6 +39,7 @@ static int pause_on_oops_flag;
 static DEFINE_SPINLOCK(pause_on_oops_lock);
 bool crash_kexec_post_notifiers;
 int panic_on_warn __read_mostly;
+static unsigned int warn_limit __read_mostly;
 
 int panic_timeout = CONFIG_PANIC_TIMEOUT;
 EXPORT_SYMBOL_GPL(panic_timeout);
@@ -47,6 +48,26 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
 
 EXPORT_SYMBOL(panic_notifier_list);
 
+#ifdef CONFIG_SYSCTL
+static struct ctl_table kern_panic_table[] = {
+	{
+		.procname       = "warn_limit",
+		.data           = &warn_limit,
+		.maxlen         = sizeof(warn_limit),
+		.mode           = 0644,
+		.proc_handler   = proc_douintvec,
+	},
+	{ }
+};
+
+static __init int kernel_panic_sysctls_init(void)
+{
+	register_sysctl_init("kernel", kern_panic_table);
+	return 0;
+}
+late_initcall(kernel_panic_sysctls_init);
+#endif
+
 static long no_blink(int state)
 {
 	return 0;
@@ -124,8 +145,14 @@ EXPORT_SYMBOL(nmi_panic);
 
 void check_panic_on_warn(const char *origin)
 {
+	static atomic_t warn_count = ATOMIC_INIT(0);
+
 	if (panic_on_warn)
 		panic("%s: panic_on_warn set ...\n", origin);
+
+	if (atomic_inc_return(&warn_count) >= READ_ONCE(warn_limit) && warn_limit)
+		panic("%s: system warned too often (kernel.warn_limit is %d)",
+		      origin, warn_limit);
 }
 
 /**