linux-kernel - [PATCH v4 2/6] printk: honor the max_reason field in kmsg

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Date:   Fri, 15 May 2020 11:44:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Kees Cook <keescook@...omium.org>, Petr Mladek <pmladek@...e.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Benson Leung <bleung@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v4 2/6] printk: honor the max_reason field in kmsg_dumper

From: Pavel Tatashin <pasha.tatashin@...een.com>

kmsg_dump() allows to dump kmesg buffer for various system events: oops,
panic, reboot, etc. It provides an interface to register a callback call
for clients, and in that callback interface there is a field "max_reason"
which gets ignored unless always_kmsg_dump is passed as kernel parameter.

Allow clients to decide max_reason, and keep the current behavior when
max_reason is not set.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
Link: https://lore.kernel.org/lkml/20200506211523.15077-2-keescook@chromium.org/
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/kmsg_dump.h |  1 +
 kernel/printk/printk.c    | 15 +++++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 3f82b5cb2d82..9826014771ab 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -26,6 +26,7 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_OOPS,
 	KMSG_DUMP_EMERG,
 	KMSG_DUMP_SHUTDOWN,
+	KMSG_DUMP_MAX
 };
 
 /**
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9a9b6156270b..a121c2255737 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3157,12 +3157,19 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 	struct kmsg_dumper *dumper;
 	unsigned long flags;
 
-	if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
-		return;
-
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
-		if (dumper->max_reason && reason > dumper->max_reason)
+		enum kmsg_dump_reason max_reason = dumper->max_reason;
+
+		/*
+		 * If client has not provided a specific max_reason, default
+		 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
+		 */
+		if (max_reason == KMSG_DUMP_UNDEF) {
+			max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
+							KMSG_DUMP_OOPS;
+		}
+		if (reason > max_reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-- 
2.20.1