On 06/08/2016 02:57 AM, Pali Rohár wrote:
Hello! Mario wrote me about two I think security problems in dell-smm-hwmon driver and I would like to ask you, how to fix them. 1) File /proc/i8k (exists only when kernel is compiled with CONFIG_I8K) exports DMI_PRODUCT_SERIAL and it can be read by ordinary user, without root permission. Normally DMI_PRODUCT_SERIAL can be read from sysfs file /sys/class/dmi/id/product_serial but only by root user. 2) Via /proc/i8k ordinary user can set fan speed. This is because how "restricted" parameter and variable works. Setting fan speed by normal non-root user can be dangerous, e.g. malicious application under user "nobody" could take control of fans. Do you have idea how to fix these problems? Just to note that /proc/i8k has stable kernel ABI and changing it will break all existing i8k* applications. But /proc/i8k is there only for old legacy laptops (year 2000). There is module parameter "restricted" with default value false and description: "Allow fan control if SYS_ADMIN capability set". Current code do: case I8K_SET_FAN: if (restricted && !capable(CAP_SYS_ADMIN)) return -EPERM; For me description is a bit ambiguous. What about setting "restricted" by default to true and updating description to something like this? "Disallow fan control when SYS_ADMIN capability is not set (default: 1)"
Sure. I am sure that someone will complain (we learned just recently that people still use the old commands, after all), but then the old behavior can be restored by setting the flag to 0. I would not use a double negative to describe it. Why not just something like "Allow fan control only if SYS_ADMIN capability set (default 1)" ? Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-hwmon" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html