Re: [Intel-gfx] [PATCH] drm: Check if primary mst is null

[Lyude Paul]

Thanks for noticing this one! With the changes that Ville mentioned in their
response:

Reviewed-by: Lyude Paul 

If you need me to push this for you; poke me here or on IRC

On Wed, 2018-11-07 at 18:11 +0200, Stanislav Lisovskiy wrote:
> Unfortunately drm_dp_get_mst_branch_device which is called from both
> drm_dp_mst_handle_down_rep and drm_dp_mst_handle_up_rep seem to rely
> on that mgr->mst_primary is not NULL, which seem to be wrong as it can be
> cleared with simultaneous mode set, if probing fails or in other case.
> mgr->lock mutex doesn't protect against that as it might just get assigned
> to NULL
> right before, not simultaneously.
> There are currently bugs 107738, 108816 bugs which crash in
> drm_dp_get_mst_branch_device, caused by this issue.
> 
> Signed-off-by: Stanislav Lisovskiy 
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 5ff1d79b86c4..fb90ed4cdc3a 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1273,6 +1273,12 @@ static struct drm_dp_mst_branch
> *drm_dp_get_mst_branch_device(struct drm_dp_mst_
>   /* find the port by iterating down */
>  
>   mutex_lock(>lock);
> +
> + if (!mgr->mst_primary) {
> + mstb = NULL;
> + goto out;
> + }
> +
>   mstb = mgr->mst_primary;
>  
>   for (i = 0; i < lct - 1; i++) {
-- 
Cheers,
Lyude Paul

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Re: [Intel-gfx] [PATCH] drm: Check if primary mst is null

[Ville Syrjälä]

On Wed, Nov 07, 2018 at 06:11:30PM +0200, Stanislav Lisovskiy wrote:
> Unfortunately drm_dp_get_mst_branch_device which is called from both
> drm_dp_mst_handle_down_rep and drm_dp_mst_handle_up_rep seem to rely
> on that mgr->mst_primary is not NULL, which seem to be wrong as it can be
> cleared with simultaneous mode set, if probing fails or in other case.
> mgr->lock mutex doesn't protect against that as it might just get assigned to 
> NULL
> right before, not simultaneously.
> There are currently bugs 107738, 108816 bugs which crash in
> drm_dp_get_mst_branch_device, caused by this issue.

Use the proper Bugzilla: tags for those. This also seems like cc:stable
material.

> 
> Signed-off-by: Stanislav Lisovskiy 
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 5ff1d79b86c4..fb90ed4cdc3a 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1273,6 +1273,12 @@ static struct drm_dp_mst_branch 
> *drm_dp_get_mst_branch_device(struct drm_dp_mst_
>   /* find the port by iterating down */
>  
>   mutex_lock(>lock);
> +
> + if (!mgr->mst_primary) {
> + mstb = NULL;
> + goto out;
> + }
> +
>   mstb = mgr->mst_primary;
>  

Or a bit simpler:

  mstb = mgr->mst_primary;
+ if (!mstb)
+   goto out;

ccing Lyude as well..

>   for (i = 0; i < lct - 1; i++) {
> -- 
> 2.17.1
> 
> ___
> dri-devel mailing list
> dri-de...@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel
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[Intel-gfx] [PATCH] drm: Check if primary mst is null

[Stanislav Lisovskiy]

Unfortunately drm_dp_get_mst_branch_device which is called from both
drm_dp_mst_handle_down_rep and drm_dp_mst_handle_up_rep seem to rely
on that mgr->mst_primary is not NULL, which seem to be wrong as it can be
cleared with simultaneous mode set, if probing fails or in other case.
mgr->lock mutex doesn't protect against that as it might just get assigned to 
NULL
right before, not simultaneously.
There are currently bugs 107738, 108816 bugs which crash in
drm_dp_get_mst_branch_device, caused by this issue.

Signed-off-by: Stanislav Lisovskiy 
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 5ff1d79b86c4..fb90ed4cdc3a 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1273,6 +1273,12 @@ static struct drm_dp_mst_branch 
*drm_dp_get_mst_branch_device(struct drm_dp_mst_
/* find the port by iterating down */
 
mutex_lock(>lock);
+
+   if (!mgr->mst_primary) {
+   mstb = NULL;
+   goto out;
+   }
+
mstb = mgr->mst_primary;
 
for (i = 0; i < lct - 1; i++) {
-- 
2.17.1

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