acpi ec_sys: Be more cautious about ec write access

- Set Kconfig option default n
- Only allow root to read/write io file (sever bug!)
- Introduce write support module param -> default off
- Properly clean up if any debugfs files cannot be created

Signed-off-by: Thomas Renninger <trenn@suse.de>
CC: mjg59@srcf.ucam.org
CC: platform-driver-x86@vger.kernel.org
CC: linux-acpi@vger.kernel.org
CC: astarikovskiy@suse.de
Signed-off-by: Matthew Garrett <mjg@redhat.com>

2 files changed, 32 insertions, 10 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index f7226d1bc80e..08e0140920e1 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -106,14 +106,19 @@ config ACPI_SYSFS_POWER
 
 config ACPI_EC_DEBUGFS
         tristate "EC read/write access through /sys/kernel/debug/ec"
-        default y
+        default n
         help
           Say N to disable Embedded Controller /sys/kernel/debug interface
 
+          Be aware that using this interface can confuse your Embedded
+          Controller in a way that a normal reboot is not enough. You then
+          have to power of your system, and remove the laptop battery for
+          some seconds.
           An Embedded Controller typically is available on laptops and reads
           sensor values like battery state and temperature.
-          The kernel access the EC through ACPI parsed code provided by BIOS
-          tables.
+          The kernel accesses the EC through ACPI parsed code provided by BIOS
+          tables. This option allows to access the EC directly without ACPI
+          code being involved.
           Thus this option is a debug option that helps to write ACPI drivers
           and can be used to identify ACPI code or EC firmware bugs.
 
diff --git a/drivers/acpi/ec_sys.c b/drivers/acpi/ec_sys.c
index 3ef978185c73..0e869b3f81ca 100644
--- a/drivers/acpi/ec_sys.c
+++ b/drivers/acpi/ec_sys.c
@@ -17,6 +17,11 @@ MODULE_AUTHOR("Thomas Renninger <trenn@suse.de>");
 MODULE_DESCRIPTION("ACPI EC sysfs access driver");
 MODULE_LICENSE("GPL");
 
+static bool write_support;
+module_param(write_support, bool, 0644);
+MODULE_PARM_DESC(write_support, "Dangerous, reboot and removal of battery may "
+                 "be needed.");
+
 #define EC_SPACE_SIZE 256
 
 struct sysdev_class acpi_ec_sysdev_class = {
@@ -102,6 +107,8 @@ int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
 {
         struct dentry *dev_dir;
         char name[64];
+        mode_t mode = 0400;
+
         if (ec_device_count == 0) {
                 acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
                 if (!acpi_ec_debugfs_dir)
@@ -111,17 +118,27 @@ int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
         sprintf(name, "ec%u", ec_device_count);
         dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
         if (!dev_dir) {
-                if (ec_device_count == 0)
-                        debugfs_remove_recursive(acpi_ec_debugfs_dir);
-                /* TBD: Proper cleanup for multiple ECs */
+                if (ec_device_count != 0)
+                        goto error;
                 return -ENOMEM;
         }
 
-        debugfs_create_x32("gpe", 0444, dev_dir, (u32 *)&first_ec->gpe);
-        debugfs_create_bool("use_global_lock", 0444, dev_dir,
-                            (u32 *)&first_ec->global_lock);
-        debugfs_create_file("io", 0666, dev_dir, ec, &acpi_ec_io_ops);
+        if (!debugfs_create_x32("gpe", 0444, dev_dir, (u32 *)&first_ec->gpe))
+                goto error;
+        if (!debugfs_create_bool("use_global_lock", 0444, dev_dir,
+                                 (u32 *)&first_ec->global_lock))
+                goto error;
+
+        if (write_support)
+                mode = 0600;
+        if (!debugfs_create_file("io", mode, dev_dir, ec, &acpi_ec_io_ops))
+                goto error;
+
         return 0;
+
+error:
+        debugfs_remove_recursive(acpi_ec_debugfs_dir);
+        return -ENOMEM;
 }
 
 static int __init acpi_ec_sys_init(void)