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>
Date:   Sun, 06 Jan 2019 13:40:30 +0100
In-Reply-To: <20190106123358.18395-1-dsugar@tresys.com> (David Sugar's message
        of "Sun, 6 Jan 2019 12:34:35 +0000")
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"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;

> +')
> +
>  ########################################
>  ## <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