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Date: Tue, 20 Feb 2018 14:53:39 +0200
From: Oleksandr Andrushchenko <andr2000@...il.com>
To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@...m.com>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
airlied@...ux.ie, daniel.vetter@...el.com
Subject: Re: [PATCH] drm/simple_kms_helper: Fix NULL pointer dereference with
no active CRTC
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@...m.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@...m.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
>
>>>> +
>>>> + 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@...m.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@...m.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@...ll.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
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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