Re: [PATCH] drm/simple_kms_helper: Fix NULL pointer dereference with no active CRTC

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Feb 20, 2018 at 02:36:05PM +0200, Oleksandr Andrushchenko wrote:
> On 02/20/2018 01:17 PM, Daniel Vetter wrote:
> > On Mon, Feb 19, 2018 at 04:58:43PM +0200, Oleksandr Andrushchenko wrote:
> > > On 02/19/2018 04:30 PM, Daniel Vetter wrote:
> > > > On Tue, Feb 13, 2018 at 10:44:16AM +0200, Oleksandr Andrushchenko wrote:
> > > > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> > > > > 
> > > > > It is possible that drm_simple_kms_plane_atomic_check called
> > > > > with no CRTC set, e.g. when user-space application sets CRTC_ID/FB_ID
> > > > > to 0 before doing any actual drawing. This leads to NULL pointer
> > > > > dereference because in this case new CRTC state is NULL and must be
> > > > > checked before accessing.
> > > > > 
> > > > > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> > > > > ---
> > > > >    drivers/gpu/drm/drm_simple_kms_helper.c | 6 ++++--
> > > > >    1 file changed, 4 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> > > > > index 9ca8a4a59b74..a05eca9cec8b 100644
> > > > > --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> > > > > +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> > > > > @@ -121,8 +121,10 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
> > > > >    	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
> > > > >    	crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
> > > > >    						   &pipe->crtc);
> > > > > -	if (!crtc_state->enable)
> > > > > -		return 0; /* nothing to check when disabling or disabled */
> > > > > +
> > > > > +	if (!crtc_state || !crtc_state->enable)
> > > > > +		/* nothing to check when disabling or disabled or no CRTC set */
> > > > > +		return 0;
> > > > >    	if (crtc_state->enable)
> > > > >    		drm_mode_get_hv_timing(&crtc_state->mode,
> > > > Hm, this is a bit annoying, since the can_position = false parameter to
> > > > drm_atomic_helper_check_plane_state is supposed to catch all this. Would
> > > > moving all the checks after the call to that helper, and gating them on
> > > > plane_state->visible also work?
> > > Yes, it does work if this is what you mean:
> > I wasn't sure, thanks for figuring this out!
> > 
> > > diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c
> > > b/drivers/gpu/drm/drm_simple_kms_helper.c
> > > index a05eca9cec8b..c48858bb2823 100644
> > > --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> > > +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> > > @@ -122,14 +122,6 @@ static int drm_simple_kms_plane_atomic_check(struct
> > > drm_plane *plane,
> > >          crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
> > > &pipe->crtc);
> > > 
> > > -       if (!crtc_state || !crtc_state->enable)
> > > -               /* nothing to check when disabling or disabled or no CRTC
> > > set */
> > > -               return 0;
> > > -
> > > -       if (crtc_state->enable)
> > > -               drm_mode_get_hv_timing(&crtc_state->mode,
> > > -                                      &clip.x2, &clip.y2);
> > > -
> > >          ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
> > >                                                    &clip,
> > > DRM_PLANE_HELPER_NO_SCALING,
> > > @@ -138,6 +130,13 @@ static int drm_simple_kms_plane_atomic_check(struct
> > > drm_plane *plane,
> > >          if (ret)
> > >                  return ret;
> > > 
> > > +       if (!plane_state->visible || !crtc_state->enable)
> > > +               return 0; /* nothing to check when disabling or disabled */
> > if (!plane_state->visible) {
> > 	WARN_ON(crtc_state->enabled);
> > 	return 0;
> > }
> > 
> > The helper call above should guarantee this.
> Yes, but I still see cases when crtc_state is NULL, thus
> making crtc_state->enable to fail

Right, when the plane is completely off there's no CRTC state. Correct
check should be

	WARN_ON(crtc_state && crtc_state->enabled);


> > > +
> > > +       if (plane_state->visible && crtc_state->enable)
> > Similar here.
> > 
> > > +               drm_mode_get_hv_timing(&crtc_state->mode,
> > > +                                      &clip.x2, &clip.y2);
> > > +
> > >          if (!plane_state->visible)
> > >                  return -EINVAL;
> > This can now be removed, the plane helper takes care of checking for
> > plane_state->visible != crtc_state->enable. Please also remove.
> > 
> > > > We'd need to add a guarantee to drm_atomic_helper_check_plane_state that
> > > > it can cope with crtc_state == NULL, but I think that's a good idea
> > > > anyway. Atm it shouldn't end up looking at the crtc_state pointer in that
> > > > case.
> > > It doesn't look at it at the moment
> > > > Otherwise we'll just go with your fix, but it feels all a bit too fragile,
> > > > hence why I want to explore more robust options a bit.
> > > At list with the change above it passes my test which failed
> > > before. Although I cannot confirm it works for others, but it
> > > certainly does for me.
> > > > -Daniel
> > > Do you want me to send v1 with the code above?
> > Yes please, with my above cleanup suggestions.
> Please see the patch under test attached (I believe it is what you mean,
> with the only change that
>     if (!plane_state->visible) {
>         *if (crtc_state)*
>             WARN_ON(crtc_state->enable);
>         return 0;
>     }
> check is used).
> 
> Whith this patch + additional logs I have:
> 
> [   18.939204] [drm:drm_ioctl [drm]] pid=2105, dev=0xe200, auth=1,
> DRM_IOCTL_MODE_ATOMIC
> [...]
> [   18.939681] [drm:drm_atomic_set_crtc_for_plane [drm]] Link plane state
> 00000000c302cbbf to [NOCRTC]
> [   18.939822] [drm:drm_atomic_set_fb_for_plane [drm]] Set [NOFB] for plane
> state 00000000c302cbbf
> [   18.939963] [drm:drm_atomic_print_state [drm]] checking 000000000bc224e7
> [   18.939988] vdispl vdispl.0: [drm] plane[29]: plane-0
> [   18.940003] vdispl vdispl.0: [drm]   crtc=(null)
> [   18.940018] vdispl vdispl.0: [drm]   fb=0
> [   18.940032] vdispl vdispl.0: [drm]   crtc-pos=0x0+0+0
> [   18.940048] vdispl vdispl.0: [drm]
> src-pos=0.000000x0.000000+0.000000+0.000000
> [   18.940067] vdispl vdispl.0: [drm]   rotation=1
> [   18.940199] [drm:drm_atomic_check_only [drm]] checking 000000000bc224e7
> [   18.940226] ================================= plane_state->visible 0
> crtc_state           (null)
> [...]
> [   18.978146] [drm:drm_atomic_set_crtc_for_plane [drm]] Link plane state
> 000000006bd50580 to [CRTC:30:crtc-0]
> [   18.978292] [drm:drm_atomic_set_fb_for_plane [drm]] Set [FB:35] for plane
> state 000000006bd50580
> [   18.978993] [drm:drm_atomic_set_mode_prop_for_crtc [drm]] Set
> [MODE:1024x768] for CRTC state 00000000e5a28f6a
> [   18.979425] [drm:drm_atomic_check_only [drm]] checking 000000000bc224e7
> [   18.979540] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> [CRTC:30:crtc-0] mode changed
> [   18.979632] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> [CRTC:30:crtc-0] enable changed
> [   18.979708] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> [CRTC:30:crtc-0] active changed
> [   18.979792] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> Updating routing for [CONNECTOR:28:Virtual-1]
> [   18.979877] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> [CONNECTOR:28:Virtual-1] using [ENCODER:31:None-31] on [CRTC:30:crtc-0]
> [   18.979960] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]]
> [CRTC:30:crtc-0] needs all connectors, enable: y, active: y
> [   18.980139] [drm:drm_atomic_add_affected_connectors [drm]] Adding all
> current connectors for [CRTC:30:crtc-0] to 000000000bc224e7
> [   18.980184] ================================= plane_state->visible 0
> crtc_state 00000000e5a28f6a
> [   18.980205] crtc_state->enable 1
> 
> *[   19.022608] WARNING: CPU: 1 PID: 2105 at
> drivers/gpu/drm/drm_simple_kms_helper.c:137
> drm_simple_kms_plane_atomic_check+0xdc/0xf8 [drm_kms_helper]*
> 
> [...]
> 
> [   19.113601] ================================= plane_state->visible 0
> crtc_state 00000000e5a28f6a
> [   19.113623] crtc_state->enable 1
> [   19.113792] WARNING: CPU: 1 PID: 2105 at
> drivers/gpu/drm/drm_simple_kms_helper.c:137
> drm_simple_kms_plane_atomic_check+0xdc/0xf8 [drm_kms_helper]
> 
> [...]
> 
> And finally
> 
> [   19.340249] ================================= plane_state->visible 0
> crtc_state 0000000036a1b1f5
> [   19.340271] crtc_state->enable 0
> 
> So, it seems that crtc_state can still be NULL if "!plane_state->visible"
> making
> NULL pointer dereference, so we need a check for that.
> Yet, !plane_state->visible && crtc_state->enable makes WARN_ON to fire
> always. So, probably we may want removing it.
> > 
> > Thanks, Daniel
> Thank you,
> Oleksandr

> From dbcce708b237740158a2c16029c56a579324f269 Mon Sep 17 00:00:00 2001
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> Date: Tue, 13 Feb 2018 10:32:20 +0200
> Subject: [PATCH] drm/simple_kms_helper: Fix NULL pointer dereference with no
>  active CRTC
> 
> It is possible that drm_simple_kms_plane_atomic_check called
> with no CRTC set, e.g. when user-space application sets CRTC_ID/FB_ID
> to 0 before doing any actual drawing. This leads to NULL pointer
> dereference because in this case new CRTC state is NULL and must be
> checked before accessing.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
>  drivers/gpu/drm/drm_simple_kms_helper.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> index 9ca8a4a59b74..f54711ff9767 100644
> --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> @@ -121,12 +121,6 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
>  	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
>  	crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
>  						   &pipe->crtc);
> -	if (!crtc_state->enable)
> -		return 0; /* nothing to check when disabling or disabled */
> -
> -	if (crtc_state->enable)
> -		drm_mode_get_hv_timing(&crtc_state->mode,
> -				       &clip.x2, &clip.y2);
>  
>  	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
>  						  &clip,
> @@ -136,8 +130,13 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
>  	if (ret)
>  		return ret;
>  
> -	if (!plane_state->visible)
> -		return -EINVAL;
> +	if (!plane_state->visible) {
> +		if (crtc_state)
> +			WARN_ON(crtc_state->enable);
> +		return 0;
> +	}
> +
> +	drm_mode_get_hv_timing(&crtc_state->mode, &clip.x2, &clip.y2);

lgtm. With or without the bikeshed to pull the crtc_state check into the
WARN_ON.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Please resubmit as a stand-alone patch, patchwork can't pull patches out
of attachments :-/
-Daniel

>  
>  	if (!pipe->funcs || !pipe->funcs->check)
>  		return 0;
> -- 
> 2.7.4
> 

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch