Stricter module param and sysfs permission checks

[Rusty Russell <rusty@rustcorp.com.au>]

CC's trimmed, this is not a virtio issue.

Joe Perches <joe@perches.com> writes:
> On Wed, 2014-03-19 at 17:07 +1030, Rusty Russell wrote:
>>   Ted: module_param(queue_depth, int, 444)
>>   Joe: 0444!
>>   Rusty: User perms >= group perms >= other perms?
>>   Joe: CLASS_ATTR, DEVICE_ATTR, SENSOR_ATTR and SENSOR_ATTR_2?
...
>>  	/* Default value instead of permissions? */			\
>> -	static int __param_perm_check_##name __attribute__((unused)) =	\
>> -	BUILD_BUG_ON_ZERO((perm) < 0 || (perm) > 0777 || ((perm) & 2))	\
>
> Now missing test for ((perm) & 2)
>
> Dunno if that was ever necessary.

Yeah, that was introduced by Alexey Dobriyan in 2006.  It didn't go
through me, though :(  New check is better.

allmodconfig says this breaks some things:

drivers/mtd/devices/docg3.c:
 	__ATTR(f##id##_dps0_protection_key, S_IWUGO, NULL, dps0_insert_key), \
	__ATTR(f##id##_dps1_protection_key, S_IWUGO, NULL, dps1_insert_key), \

drivers/regulator/virtual.c:
static DEVICE_ATTR(min_microvolts, 0666, show_min_uV, set_min_uV);
static DEVICE_ATTR(max_microvolts, 0666, show_max_uV, set_max_uV);
static DEVICE_ATTR(min_microamps, 0666, show_min_uA, set_min_uA);
static DEVICE_ATTR(max_microamps, 0666, show_max_uA, set_max_uA);
static DEVICE_ATTR(mode, 0666, show_mode, set_mode);

drivers/hid/hid-lg4ff.c:
static DEVICE_ATTR(range, S_IRWXU | S_IRWXG | S_IRWXO, lg4ff_range_show, lg4ff_range_store);

drivers/scsi/pm8001/pm8001_ctl.c:
static DEVICE_ATTR(update_fw, S_IRUGO|S_IWUGO,
	pm8001_show_update_fw, pm8001_store_update_fw);

... plus some staging.

So I've left that for a future patch.

Thanks,
Rusty.