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SubjectRe: [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction
On Wed, Apr 19, 2017 at 4:43 PM, Kees Cook <keescook@chromium.org> wrote:
> On Wed, Apr 19, 2017 at 4:15 PM, Andy Lutomirski <luto@kernel.org> wrote:
>> On Wed, Apr 19, 2017 at 3:20 PM, Djalal Harouni <tixxdz@gmail.com> wrote:
>>> +/* Sets task's modules_autoload */
>>> +static inline int task_set_modules_autoload(struct task_struct *task,
>>> + unsigned long value)
>>> +{
>>> + if (value > MODULES_AUTOLOAD_DISABLED)
>>> + return -EINVAL;
>>> + else if (task->modules_autoload > value)
>>> + return -EPERM;
>>> + else if (task->modules_autoload < value)
>>> + task->modules_autoload = value;
>>> +
>>> + return 0;
>>> +}
>>
>> This needs to be more locked down. Otherwise someone could set this
>> and then run a setuid program. Admittedly, it would be quite odd if
>> this particular thing causes a problem, but the issue exists
>> nonetheless.
>
> Eeeh, I don't agree this needs to be changed. APIs provided by modules
> are different than the existing privilege-manipulation syscalls this
> concern stems from. Applications are already forced to deal with
> things being missing like this in the face of it simply not being
> built into the kernel.
>
> Having to hide this behind nnp seems like it'd reduce its utility...
>

I think that adding an inherited boolean to task_struct that can be
set by unprivileged tasks and passed to privileged tasks is a terrible
precedent. Ideally someone would try to find all the existing things
like this and kill them off.

I agree that I don't see how one would exploit this particular
feature, but I still think I dislike the approach. This is a slippery
slope to adding a boolean for perf_event_open(), unshare(), etc, and
we should solve these for real rather than half-arsing them IMO.

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