[PATCH] dmi-id: Add parameter to relax sysfs permissions

[Richard Weinberger]

Every few years I find myself in a discussion that goes like:

user: I hate using dmidecode to read vendor infos, it needs root!
me: Just use /sys/class/dmi/id/
user: wow! Neat!
*later*
user: But, I can't read from product_serial!
me: *grrrr*

For systems where no confidential information is stored in the DMI IDs
allow setting the kernel module parameter dmi_id.relaxed_perms to y.
It will make sure the every sysfs attribute has at least 0444
permissions.

Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
 drivers/firmware/dmi-id.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/dmi-id.c b/drivers/firmware/dmi-id.c
index d19c78a78ae3a..a237caf89d526 100644
--- a/drivers/firmware/dmi-id.c
+++ b/drivers/firmware/dmi-id.c
@@ -12,6 +12,8 @@
 #include <linux/device.h>
 #include <linux/slab.h>
 
+static bool relaxed_perms;
+
 struct dmi_device_attribute{
 	struct device_attribute dev_attr;
 	int field;
@@ -183,10 +185,14 @@ static struct class dmi_class = {
 static struct device *dmi_dev;
 
 /* Initialization */
-
-#define ADD_DMI_ATTR(_name, _field) \
-	if (dmi_get_system_info(_field)) \
-		sys_dmi_attributes[i++] = &sys_dmi_##_name##_attr.dev_attr.attr;
+#define ADD_DMI_ATTR(_name, _field)						\
+	({									\
+	if (dmi_get_system_info(_field)) {					\
+		if (relaxed_perms)						\
+			sys_dmi_##_name##_attr.dev_attr.attr.mode |= 0444;	\
+		sys_dmi_attributes[i++] = &sys_dmi_##_name##_attr.dev_attr.attr;\
+	}									\
+	})
 
 /* In a separate function to keep gcc 3.2 happy - do NOT merge this in
    dmi_id_init! */
@@ -260,5 +266,6 @@ static int __init dmi_id_init(void)
 
 	return ret;
 }
-
+module_param(relaxed_perms, bool, 0400);
+MODULE_PARM_DESC(relaxed_perms, "Allow everyone read access to all IDs");
 arch_initcall(dmi_id_init);
-- 
2.51.0