Currently, the Linux kernel provides two types of reaction to kernel
warnings:
1. Do nothing (by default),
2. Call panic() if panic_on_warn is set. That's a very strong reaction,
so panic_on_warn is usually disabled on production systems.
>From a safety point of view, the Linux kernel misses a middle way of
handling kernel warnings:
- The kernel should stop the activity that provokes a warning,
- But the kernel should avoid complete denial of service.
>From a security point of view, kernel warning messages provide a lot of
useful information for attackers. Many GNU/Linux distributions allow
unprivileged users to read the kernel log, so attackers use kernel
warning infoleak in vulnerability exploits. See the examples:
https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html
Let's introduce the pkill_on_warn boot parameter.
If this parameter is set, the kernel kills all threads in a process
that provoked a kernel warning. This behavior is reasonable from a safety
point of view described above. It is also useful for kernel security
hardening because the system kills an exploit process that hits a
kernel warning.
Signed-off-by: Alexander Popov <alex.popov@xxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
kernel/panic.c | 5 +++++
2 files changed, 9 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..86c748907666 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4112,6 +4112,10 @@
pirq= [SMP,APIC] Manual mp-table setup
See Documentation/x86/i386/IO-APIC.rst.
+ pkill_on_warn= Kill all threads in a process that provoked a
+ kernel warning.
+ Format: { "0" | "1" }
+
plip= [PPT,NET] Parallel port network link
Format: { parport<nr> | timid | 0 }
See also Documentation/admin-guide/parport.rst.
diff --git a/kernel/panic.c b/kernel/panic.c
index cefd7d82366f..47b728bfb1d3 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -53,6 +53,7 @@ static int pause_on_oops_flag;
static DEFINE_SPINLOCK(pause_on_oops_lock);
bool crash_kexec_post_notifiers;
int panic_on_warn __read_mostly;
+int pkill_on_warn __read_mostly;
unsigned long panic_on_taint;
bool panic_on_taint_nousertaint = false;
@@ -610,6 +611,9 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
print_oops_end_marker();
+ if (pkill_on_warn && system_state >= SYSTEM_RUNNING)
+ do_group_exit(SIGKILL);
+
/* Just a warning, don't kill lockdep. */
add_taint(taint, LOCKDEP_STILL_OK);
}
@@ -694,6 +698,7 @@ core_param(panic, panic_timeout, int, 0644);
core_param(panic_print, panic_print, ulong, 0644);
core_param(pause_on_oops, pause_on_oops, int, 0644);
core_param(panic_on_warn, panic_on_warn, int, 0644);
+core_param(pkill_on_warn, pkill_on_warn, int, 0644);
core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644);
static int __init oops_setup(char *s)
--
2.31.1
