From:   Dominick Grift <dac.override@gmail.com>
To:     "Sugar\, David" <dsugar@tresys.com>
Cc:     "selinux-refpolicy\@vger.kernel.org" 
        <selinux-refpolicy@vger.kernel.org>
Subject: Re: [PATCH 1/2 v2] Allow greeter to start dbus
References: <20190106123358.18395-1-dsugar@tresys.com>
        <87d0pa7ydd.fsf@gmail.com>
        <bb6ad7ff-4904-fd32-3b3f-760e75e3ca6f@tresys.com>
Date:   Sun, 06 Jan 2019 13:54:55 +0100
In-Reply-To: <bb6ad7ff-4904-fd32-3b3f-760e75e3ca6f@tresys.com> (David Sugar's
        message of "Sun, 6 Jan 2019 12:50:47 +0000")
Message-ID: <874lam7xpc.fsf@gmail.com>
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"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 d=
omain.
>>>
>>> type=3DAVC msg=3Daudit(1544626796.378:201): avc:  denied  { execute } f=
or  pid=3D9973 comm=3D"dbus-launch" name=3D"dbus-daemon" dev=3D"dm-1" ino=
=3D6695040 scontext=3Dsystem_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=3Dsys=
tem_u:object_r:dbusd_exec_t:s0 tclass=3Dfile permissive=3D1
>>> type=3DAVC msg=3Daudit(1544626796.378:201): avc:  denied  { read open }=
 for  pid=3D9973 comm=3D"dbus-launch" path=3D"/usr/bin/dbus-daemon" dev=3D"=
dm-1" ino=3D6695040 scontext=3Dsystem_u:system_r:xdm_t:s0-s0:c0.c1023 tcont=
ext=3Dsystem_u:object_r:dbusd_exec_t:s0 tclass=3Dfile permissive=3D1
>>> type=3DAVC msg=3Daudit(1544626796.378:201): avc:  denied  { execute_no_=
trans } for  pid=3D9973 comm=3D"dbus-launch" path=3D"/usr/bin/dbus-daemon" =
dev=3D"dm-1" ino=3D6695040 scontext=3Dsystem_u:system_r:xdm_t:s0-s0:c0.c102=
3 tcontext=3Dsystem_u:object_r:dbusd_exec_t:s0 tclass=3Dfile permissive=3D1
>>> type=3DAVC msg=3Daudit(1544626796.378:201): avc:  denied  { map } for  =
pid=3D9973 comm=3D"dbus-daemon" path=3D"/usr/bin/dbus-daemon" dev=3D"dm-1" =
ino=3D6695040 scontext=3Dsystem_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=3D=
system_u:object_r:dbusd_exec_t:s0 tclass=3Dfile permissive=3D1
>>> type=3DAVC msg=3Daudit(1546551459.112:208): avc:  denied  { getcap } fo=
r pid=3D6275 comm=3D"dbus-daemon" scontext=3Dsystem_u:system_r:xdm_t:s0-s0:=
c0.c1023 tcontext=3Dsystem_u:system_r:xdm_t:s0-s0:c0.c1023 tclass=3Dprocess=
 permissive=3D1
>>>
>>> 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',`
>>>   	')
>>>   ')
>>>=20=20=20
>>> +########################################
>>> +## <summary>
>>> +##	Execute dbus in the caller domain.
>>> +## </summary>
>>> +## <param name=3D"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=20
> getcap permission not lightdm.=C2=A0 So other processes that use the=20
> dbus_exec interface will also need this permission.=C2=A0 I'm happy separ=
ate=20
> just worry it won't be clear why getcap will be added in several places=20
> 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/servic=
es/xserver.te
>>> index fa7ce88e..cc717e7f 100644
>>> --- a/policy/modules/services/xserver.te
>>> +++ b/policy/modules/services/xserver.te
>>> @@ -566,6 +566,7 @@ optional_policy(`
>>>   ')
>>>=20=20=20
>>>   optional_policy(`
>>> +	dbus_exec(xdm_t)
>>>   	dbus_system_bus_client(xdm_t)
>>>   	dbus_connect_system_bus(xdm_t)

--=20
Key fingerprint =3D 5F4D 3CDB D3F8 3652 FBD8 02D5 3B6C 5F1D 2C7B 6B02
https://sks-keyservers.net/pks/lookup?op=3Dget&search=3D0x3B6C5F1D2C7B6B02
Dominick Grift