On Wednesday 08 June 2016 15:24:10 Guenter Roeck wrote: > 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. Either setting that flag to 0 or running that tool under root or with capability CAP_SYS_ADMIN. > 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)" ? I was thinking about that description too, but there is problem with meaning too... 0 means fan control is allowed for any user 1 means fan control is allowed only for CAP_SYS_ADMIN Description should be unambiguous for situation when flag is set to 0. === And do you have idea what to do with problem 1)? -- Pali Rohár pali.rohar@xxxxxxxxx
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