[refpolicy] [PATCH] Allow getty the sys_admin capability

[dac.override@gmail.com (Dominick Grift)]

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On 03/05/2016 01:18 PM, Nicolas Iooss wrote:
> On 03/04/2016 04:54 PM, Dominick Grift wrote:
>> On 03/04/2016 02:11 PM, Christopher J. PeBenito wrote:
>>> On 3/3/2016 9:05 PM, Luis Ressel wrote:
>>>> It's required for agetty on kernels with a recent grsecurity 
>>>> patchset. (The denial itself has been showing up for quite
>>>> some time, but it hasn't had any obvious ill effects until
>>>> recently.)
>> 
>>> I'm reluctant to add this because it is a significant
>>> permission and grsecurity is not commonly used with SELinux, to
>>> my knowledge.
>> 
>> 
>> My getty requests this permission as well [1] and i am not using 
>> grsecurity. Although, i am not sure if the permission is
>> absolutely needed. (then again I do not believe that it requests
>> it for its health alone)
> 
> Hello, as I was wondering what was behind agetty requiring
> sys_admin capabilities and what would happen if the access is
> denied, I took a look to its source code.  The TIOCSTI ioctl (the
> mechanism which allows injecting characters in a terminal input
> queue) seems to only been used in a function named
> wait_for_term_input [1].  This allows the user input to be seen as
> a "normal input" while wait_for_term_input temporarily configured
> the terminal with ICANON, ECHO... attributes disabled.
> 
> If the ioctl(fd, TIOCSTI, buffer + i) call fails (for example
> because sys_admin is not granted by SELinux), this is silently
> ignored.  As far as I understand the code, wait_for_term_input
> function is only used at the beginning of the login prompt (the
> characters are echoed to the terminal) and not the password prompt.
> Therefore the user may get the feeling that the first typed
> character has been dropped somewhere.  Is that so? Are there other
> annoyances that I missed in my quick analysis?
> 
> Anyway, before grsecurity added a test for sys_admin when a process
> uses TIOCSTI ioctl on its own tty, the capability has already been
> granted when distro_redhat is enabled.  The comment which is
> associated to this access, "getty requires sys_admin #209426", is
> not clear to me.  Where could I find more information about this
> bug report?
> 

Seems to be a private bug report

https://bugzilla.redhat.com/show_bug.cgi?id=209426

I personally am of the opinion that we generally should not decide
what a process can and cannot do. If it requests it, and if it is not
a bug then I think it should be allowed.

> Cheers, Nicolas
> 
> [1] 
> https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/term-
utils/agetty.c?h=v2.27.1#n1659
>
> 
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Dominick Grift
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