[PATCH v2 5/6] panic: Introduce warn_limit

From: Kees Cook
Date: Wed Nov 09 2022 - 15:01:26 EST


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

Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: tangmeng <tangmeng@xxxxxxxxxxxxx>
Cc: "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>
Cc: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/kernel.rst | 9 +++++++++
kernel/panic.c | 13 +++++++++++++
2 files changed, 22 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 09f3fb2f8585..c385d5319cdf 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1508,6 +1508,15 @@ 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 or 1 has the same effect
+as setting ``panic_on_warn=1``.
+
+
watchdog
========

diff --git a/kernel/panic.c b/kernel/panic.c
index 3afd234767bc..b235fa4a6fc8 100644
--- a/kernel/panic.c
+++ b/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 = 10000;

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 +211,13 @@ static void panic_print_sys_info(bool console_flush)

void check_panic_on_warn(const char *reason)
{
+ static atomic_t warn_count = ATOMIC_INIT(0);
+
if (panic_on_warn)
panic("%s: panic_on_warn set ...\n", reason);
+
+ if (atomic_inc_return(&warn_count) >= READ_ONCE(warn_limit))
+ panic("Warned too often (warn_limit is %d)", warn_limit);
}

/**
--
2.34.1