Re: [PATCH] sysrq: add optional logging of caller info on /proc/sysrq-trigger write

Greg KH
2026-04-18T07:20:46Z

On Thu, Apr 16, 2026 at 09:14:19PM +0800, Xiang Gao wrote:
> From: Xiang Gao <gaoxiang17@xiaomi.com>
>
> When /proc/sysrq-trigger is written to, there is no record of which
> process triggered the sysrq operation. This makes it difficult to audit
> or debug who initiated a sysrq action, especially when the write comes
> from a shell spawned by system()/popen() where the immediate caller is
> "sh" rather than the originating application.
>
> Add CONFIG_MAGIC_SYSRQ_TRIGGER_LOG (default n) and a runtime toggle via
> module parameter sysrq.trigger_log (default off). When both are enabled,
> the kernel logs the triggering process's comm, pid, tgid, uid, and walks
> up to 5 levels of the parent process chain. This allows tracing the
> original initiator even through system()/popen()/fork+exec indirection.
>
> Example output:
> sysrq: proc trigger: comm=sh pid=68 tgid=68 uid=0
> sysrq: parent[0]: comm=my_app pid=67 tgid=67
> sysrq: parent[1]: comm=init pid=1 tgid=1
>
> Usage:
> # Compile-time: enable CONFIG_MAGIC_SYSRQ_TRIGGER_LOG=y
> # Runtime: echo 1 > /sys/module/sysrq/parameters/trigger_log
> # Or boot parameter: sysrq.trigger_log=1
>
> Signed-off-by: Xiang Gao <gaoxiang17@xiaomi.com>
> ---
> drivers/tty/sysrq.c | 29 +++++++++++++++++++++++++++++
> lib/Kconfig.debug | 16 ++++++++++++++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index c2e4b31b699a..e9277e7de35b 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -48,6 +48,9 @@
> #include <linux/uaccess.h>
> #include <linux/moduleparam.h>
> #include <linux/jiffies.h>
> +#ifdef CONFIG_MAGIC_SYSRQ_TRIGGER_LOG
> +#include <linux/cred.h>
> +#endif

We really do not want or like #ifdef in .c files, and for stuff like
this, it is not needed at all.

> #include <linux/syscalls.h>
> #include <linux/of.h>
> #include <linux/rcupdate.h>
> @@ -59,6 +62,12 @@
> static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
> static bool __read_mostly sysrq_always_enabled;
>
> +#ifdef CONFIG_MAGIC_SYSRQ_TRIGGER_LOG
> +static bool sysrq_trigger_log;
> +module_param_named(trigger_log, sysrq_trigger_log, bool, 0644);
> +MODULE_PARM_DESC(trigger_log, "Log caller info on /proc/sysrq-trigger write");
> +#endif

Module parameters are really not the way for stuff like this. And why
would such a "tiny" option need a config option at all? If you don't
use/need it, it's only a single bool being used?

> +
> static bool sysrq_on(void)
> {
> return sysrq_enabled || sysrq_always_enabled;
> @@ -1209,6 +1218,26 @@ static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
> bool bulk = false;
> size_t i;
>
> +#ifdef CONFIG_MAGIC_SYSRQ_TRIGGER_LOG
> + if (sysrq_trigger_log) {
> + struct task_struct *task;
> + int depth = 0;
> +
> + pr_info("proc trigger: comm=%s pid=%d tgid=%d uid=%u\n",
> + current->comm, current->pid, current->tgid,
> + from_kuid(&init_user_ns, current_uid()));

The kernel log is not there for doing audits and the like, so is this
just a debug option?

> +
> + rcu_read_lock();
> + task = current;
> + while (task->pid > 1 && depth < 5) {
> + task = rcu_dereference(task->real_parent);
> + pr_info(" parent[%d]: comm=%s pid=%d tgid=%d\n",
> + depth++, task->comm, task->pid, task->tgid);
> + }
> + rcu_read_unlock();

This might cause problems for when the system is hung and sysrq is the
only way to reboot the box. Have you tried it in that situation?

> + }
> +#endif
> +
> for (i = 0; i < count; i++) {
> char c;
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index aac60b6cfa4b..46bd361decd0 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -705,6 +705,22 @@ config MAGIC_SYSRQ_SERIAL_SEQUENCE
>
> If unsure, leave an empty string and the option will not be enabled.
>
> +config MAGIC_SYSRQ_TRIGGER_LOG
> + bool "Log caller info on /proc/sysrq-trigger write"
> + depends on MAGIC_SYSRQ
> + default n

n is always the default, no need to add it again.

thanks,

greg k-h