[PATCH v2 2/2] hibernate: split snapshot dev option

[Domenico Andreoli <domenico.andreoli@linux.com>]

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From: Domenico Andreoli <domenico.andreoli@linux.com>

Make it possible to reduce the attack surface in case the snapshot
device is not to be used from userspace.

v2:
 - the option is enabled by default (it was disabled by default)
 - remove the premature "DEPRECATED" marking
 - drop the redefinition of mutual exclusion helpers (in v2 they are
   owned by hibernte.c) in case the option is deselected
 - add the help message to the config option

Signed-off-by: Domenico Andreoli <domenico.andreoli@linux.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Linux PM <linux-pm@vger.kernel.org>

---
 kernel/power/Kconfig  |   12 ++++++++++++
 kernel/power/Makefile |    3 ++-
 2 files changed, 14 insertions(+), 1 deletion(-)

Index: b/kernel/power/Kconfig
===================================================================
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -80,6 +80,18 @@ config HIBERNATION
 
 	  For more information take a look at <file:Documentation/power/swsusp.rst>.
 
+config HIBERNATION_SNAPSHOT_DEV
+	bool "Userspace snapshot device"
+	depends on HIBERNATION
+	default y
+	---help---
+	  Device used by the uswsusp tools.
+
+	  Say N if no snapshotting from userspace is needed, this also
+	  reduces the attack surface of the kernel.
+
+	  If in doubt, say Y.
+
 config PM_STD_PARTITION
 	string "Default resume partition"
 	depends on HIBERNATION
Index: b/kernel/power/Makefile
===================================================================
--- a/kernel/power/Makefile
+++ b/kernel/power/Makefile
@@ -10,7 +10,8 @@ obj-$(CONFIG_VT_CONSOLE_SLEEP)	+= consol
 obj-$(CONFIG_FREEZER)		+= process.o
 obj-$(CONFIG_SUSPEND)		+= suspend.o
 obj-$(CONFIG_PM_TEST_SUSPEND)	+= suspend_test.o
-obj-$(CONFIG_HIBERNATION)	+= hibernate.o snapshot.o swap.o user.o
+obj-$(CONFIG_HIBERNATION)	+= hibernate.o snapshot.o swap.o
+obj-$(CONFIG_HIBERNATION_SNAPSHOT_DEV) += user.o
 obj-$(CONFIG_PM_AUTOSLEEP)	+= autosleep.o
 obj-$(CONFIG_PM_WAKELOCKS)	+= wakelock.o