Re: [PATCH 1/2 v2] Allow greeter to start dbus

[Dominick Grift <dac.override@gmail.com>]

"Sugar, David" <dsugar@tresys.com> writes:

> On 1/6/19 7:40 AM, Dominick Grift wrote:
>> "Sugar, David" <dsugar@tresys.com> writes:
>>
>>> The display manager lightdm (and I think gdm) start a dbus binary.
>>>
>>> This adds (and uses) new interface dbus_exec to start dbus in the xdm domain.
>>>
>>> type=AVC msg=audit(1544626796.378:201): avc:  denied  { execute } for  pid=9973 comm="dbus-launch" name="dbus-daemon" dev="dm-1" ino=6695040 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:object_r:dbusd_exec_t:s0 tclass=file permissive=1
>>> type=AVC msg=audit(1544626796.378:201): avc:  denied  { read open } for  pid=9973 comm="dbus-launch" path="/usr/bin/dbus-daemon" dev="dm-1" ino=6695040 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:object_r:dbusd_exec_t:s0 tclass=file permissive=1
>>> type=AVC msg=audit(1544626796.378:201): avc:  denied  { execute_no_trans } for  pid=9973 comm="dbus-launch" path="/usr/bin/dbus-daemon" dev="dm-1" ino=6695040 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:object_r:dbusd_exec_t:s0 tclass=file permissive=1
>>> type=AVC msg=audit(1544626796.378:201): avc:  denied  { map } for  pid=9973 comm="dbus-daemon" path="/usr/bin/dbus-daemon" dev="dm-1" ino=6695040 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:object_r:dbusd_exec_t:s0 tclass=file permissive=1
>>> type=AVC msg=audit(1546551459.112:208): avc:  denied  { getcap } for pid=6275 comm="dbus-daemon" scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tclass=process permissive=1
>>>
>>> Signed-off-by: Dave Sugar <dsugar@tresys.com>
>>> ---
>>>   policy/modules/services/dbus.if    | 21 +++++++++++++++++++++
>>>   policy/modules/services/xserver.te |  1 +
>>>   2 files changed, 22 insertions(+)
>>>
>>> diff --git a/policy/modules/services/dbus.if b/policy/modules/services/dbus.if
>>> index ef829e30..d0eec745 100644
>>> --- a/policy/modules/services/dbus.if
>>> +++ b/policy/modules/services/dbus.if
>>> @@ -17,6 +17,27 @@ interface(`dbus_stub',`
>>>   	')
>>>   ')
>>>   
>>> +########################################
>>> +## <summary>
>>> +##	Execute dbus in the caller domain.
>>> +## </summary>
>>> +## <param name="domain">
>>> +## <summary>
>>> +##	Domain allowed access.
>>> +## </summary>
>>> +## </param>
>>> +#
>>> +interface(`dbus_exec',`
>>> +	gen_require(`
>>> +		type dbusd_exec_t;
>>> +	')
>>> +
>>> +	corecmd_search_bin($1)
>>> +	can_exec($1, dbusd_exec_t)
>>> +
>>> +	allow $1 self:process getcap;
>> I would not enclose the getcap rule here. For example I do not believe
>> you need that permission to be able to `dbus-daemon --version`. Instead I
>> would add that rule to xserver.te:
>>
>> allow xdm_t self:process getcap;
>
> I did it this way due to the fact that it is dbus-daemon needing the 
> getcap permission not lightdm.  So other processes that use the 
> dbus_exec interface will also need this permission.  I'm happy separate 
> just worry it won't be clear why getcap will be added in several places 
> due to this.
>

`dbus-daemon --version` does not seem to require getcap

executing dbus potentially requires many permissions but that does not
mean that we should add these permissions to dbus_exec()

>>> +')
>>> +
>>>   ########################################
>>>   ## <summary>
>>>   ##	Role access for dbus.
>>> diff --git a/policy/modules/services/xserver.te b/policy/modules/services/xserver.te
>>> index fa7ce88e..cc717e7f 100644
>>> --- a/policy/modules/services/xserver.te
>>> +++ b/policy/modules/services/xserver.te
>>> @@ -566,6 +566,7 @@ optional_policy(`
>>>   ')
>>>   
>>>   optional_policy(`
>>> +	dbus_exec(xdm_t)
>>>   	dbus_system_bus_client(xdm_t)
>>>   	dbus_connect_system_bus(xdm_t)

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Dominick Grift