[PATCH] drm/simple_kms_helper: Fix NULL pointer dereference with no active CRTC
Oleksandr Andrushchenko
Oleksandr_Andrushchenko at epam.com
Mon Mar 5 08:55:54 UTC 2018
On 03/05/2018 10:52 AM, Daniel Vetter wrote:
> On Tue, Feb 20, 2018 at 03:29:07PM +0200, Oleksandr Andrushchenko wrote:
>> On 02/20/2018 02:53 PM, Oleksandr Andrushchenko wrote:
>>> On 02/20/2018 02:49 PM, Daniel Vetter wrote:
>>>> 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 at 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 at 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);
>>> ok, will update with this additional check
>> huh, this indeed solves the NULL pointer dereference, but floods a lot
>> with every page flip I have, e.g. !plane_state->visible == true
>> and crtc_state is not NULL and crtc_state->enable == true,
>> thus firing WARN_ON.
>> Is this something wrong with my use-case/driver or it is still legal
>> to have such a configuration and leave it without WARN_ON and just
>> return 0?
> 1 week of vacation later I have to admit that this WARN_ON is completely
> bogus :-)
np ;)
> Sorry for all the confusion, pls leave it out.
> -Daniel
>
>>>>>>> +
>>>>>>> + 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 at 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 at 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 at ffwll.ch>
>>> Thank you
>>>> Please resubmit as a stand-alone patch, patchwork can't pull patches out
>>>> of attachments :-/
>>> oh, that was for demonstration purpose only, so we
>>> are on the same page and see the patch we are discussing ;)
>>>> -Daniel
>>>>
>>>>> if (!pipe->funcs || !pipe->funcs->check)
>>>>> return 0;
>>>>> --
>>>>> 2.7.4
>>>>>
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