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From:   Vincent Whitchurch <vincent.whitchurch@axis.com>
To:     akpm@linux-foundation.org
Cc:     mcgrof@kernel.org, keescook@chromium.org,
        linux-kernel@vger.kernel.org, Vincent Whitchurch <rabinv@axis.com>
Subject: [PATCH v2] sysctl: Add panic-fatal-signals
Date:   Mon, 28 Jan 2019 09:49:59 +0100
Message-Id: <20190128084959.13060-1-vincent.whitchurch@axis.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Add a sysctl which asks the kernel to panic when any userspace process
receives a fatal signal which would trigger a core dump.  This has
proven to be quite useful when debugging problems seen during testing of
embedded systems:  When combined with kernel core dumps (saved due to
the panic), it allows easier debugging of crashes which have their
origin in system-wide problems such as buggy drivers or other kernel or
hardware-related issues.

The crashing process's core dump can be extracted from the kernel core
dump using tools such as the crash utility's gcore extension.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
v2: Put the sysctl behind a config option

 include/linux/signal.h |  1 +
 init/Kconfig           | 14 ++++++++++++++
 kernel/signal.c        |  5 ++++-
 kernel/sysctl.c        |  9 +++++++++
 4 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index cc7e2c1cd444..109efd1432e9 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -10,6 +10,7 @@ struct task_struct;
 
 /* for sysctl */
 extern int print_fatal_signals;
+extern int panic_fatal_signals;
 
 static inline void copy_siginfo(kernel_siginfo_t *to,
 				const kernel_siginfo_t *from)
diff --git a/init/Kconfig b/init/Kconfig
index d47cb77a220e..875442f6ab53 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1242,6 +1242,20 @@ config SYSCTL_SYSCALL
 
 	  If unsure say N here.
 
+config SYSCTL_PANIC_FATAL_SIGNALS
+	bool "panic-fatal-signals sysctl" if EXPERT
+	depends on PROC_SYSCTL
+	help
+	  If you say Y here, a kernel.panic-fatal-signals sysctl will be
+	  offered.  If this sysctl is turned on, the kernel will panic if any
+	  userspace process receives a fatal signal which would trigger a core
+	  dump.
+
+	  When used together with kernel core dumps, this can be useful for
+	  debugging some system-wide problems, primarily on embedded systems.
+
+	  If unsure, say N.
+
 config FHANDLE
 	bool "open by fhandle syscalls" if EXPERT
 	select EXPORTFS
diff --git a/kernel/signal.c b/kernel/signal.c
index e1d7ad8e6ab1..83c6877b0182 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -59,6 +59,7 @@
 static struct kmem_cache *sigqueue_cachep;
 
 int print_fatal_signals __read_mostly;
+int panic_fatal_signals __read_mostly;
 
 static void __user *sig_handler(struct task_struct *t, int sig)
 {
@@ -2497,8 +2498,10 @@ bool get_signal(struct ksignal *ksig)
 		current->flags |= PF_SIGNALED;
 
 		if (sig_kernel_coredump(signr)) {
-			if (print_fatal_signals)
+			if (print_fatal_signals || panic_fatal_signals)
 				print_fatal_signal(ksig->info.si_signo);
+			if (panic_fatal_signals)
+				panic("Fatal signal and panic_fatal_signals=1");
 			proc_coredump_connector(current);
 			/*
 			 * If it was able to dump core, this kills all
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ba4d9e85feb8..48023bad5b08 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -557,6 +557,15 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+#ifdef CONFIG_SYSCTL_PANIC_FATAL_SIGNALS
+	{
+		.procname	= "panic-fatal-signals",
+		.data		= &panic_fatal_signals,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+#endif
 #ifdef CONFIG_SPARC
 	{
 		.procname	= "reboot-cmd",
-- 
2.20.0