[PATCH 5.4 14/17] panic: Introduce warn_limit

[Eric Biggers <ebiggers@kernel.org>]

From: Kees Cook <keescook@chromium.org>

commit 9fc9e278a5c0b708eeffaf47d6eb0c82aa74ed78 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>
---
 Documentation/admin-guide/sysctl/kernel.rst | 10 ++++++++
 kernel/panic.c                              | 27 +++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index bc31c4a88f20f..568c24ff00a72 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1186,6 +1186,16 @@ 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:
 =========
 
diff --git a/kernel/panic.c b/kernel/panic.c
index 7e4900eb25ac1..8f72305dd501d 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -44,6 +44,7 @@ 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);
@@ -60,6 +61,26 @@ 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;
@@ -158,8 +179,14 @@ static void panic_print_sys_info(void)
 
 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);
 }
 
 /**
-- 
2.39.1