panic: Introduce warn_limit

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

Cc: Jonathan Corbet <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: "Jason A. Donenfeld" <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: tangmeng <[email protected]>
Cc: "Guilherme G. Piccoli" <[email protected]>
Cc: Tiezhu Yang <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: [email protected]
Reviewed-by: Luis Chamberlain <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: kees

Documentation/admin-guide/sysctl/kernel.rst

@@ -1509,6 +1509,16 @@ entry will default to 2 instead of 0.
 2 Unprivileged calls to ``bpf()`` are disabled
 = =============================================================
 
+
+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
 ========
 

kernel/panic.c

@@ -58,6 +58,7 @@ bool crash_kexec_post_notifiers;
 int panic_on_warn __read_mostly;
 unsigned long panic_on_taint;
 bool panic_on_taint_nousertaint = false;
+static unsigned int warn_limit __read_mostly;
 
 int panic_timeout = CONFIG_PANIC_TIMEOUT;
 EXPORT_SYMBOL_GPL(panic_timeout);
@@ -88,6 +89,13 @@ static struct ctl_table kern_panic_table[] = {
 		.extra2         = SYSCTL_ONE,
 	},
 #endif
+	{
+		.procname       = "warn_limit",
+		.data           = &warn_limit,
+		.maxlen         = sizeof(warn_limit),
+		.mode           = 0644,
+		.proc_handler   = proc_douintvec,
+	},
 	{ }
 };
 
@@ -203,8 +211,14 @@ static void panic_print_sys_info(bool console_flush)
 
 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);
 }
 
 /**