[PATCH AUTOSEL 5.4 102/175] drm/vkms: Hold gem object while still in-use

Sasha Levin
2020-06-09T00:06:50Z

From: Ezequiel Garcia <ezequiel@collabora.com>

[ Upstream commit 0ea2ea42b31abc1141f2fd3911f952a97d401fcb ]

We need to keep the reference to the drm_gem_object
until the last access by vkms_dumb_create.

Therefore, the put the object after it is used.

This fixes a use-after-free issue reported by syzbot.

While here, change vkms_gem_create() symbol to static.

Reported-and-tested-by: syzbot+e3372a2afe1e7ef04bc7@syzkaller.appspotmail.com
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200427214405.13069-1-ezequiel@collabora.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/vkms/vkms_drv.h | 5 -----
drivers/gpu/drm/vkms/vkms_gem.c | 11 ++++++-----
2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index 5a95100fa18b..03b05c54722d 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -121,11 +121,6 @@ struct drm_plane *vkms_plane_init(struct vkms_device *vkmsdev,
enum drm_plane_type type, int index);

/* Gem stuff */
-struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
- struct drm_file *file,
- u32 *handle,
- u64 size);
-
vm_fault_t vkms_gem_fault(struct vm_fault *vmf);

int vkms_dumb_create(struct drm_file *file, struct drm_device *dev,
diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
index 6489bfe0a149..8ba8b87d0c99 100644
--- a/drivers/gpu/drm/vkms/vkms_gem.c
+++ b/drivers/gpu/drm/vkms/vkms_gem.c
@@ -95,10 +95,10 @@ vm_fault_t vkms_gem_fault(struct vm_fault *vmf)
return ret;
}

-struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
- struct drm_file *file,
- u32 *handle,
- u64 size)
+static struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
+ struct drm_file *file,
+ u32 *handle,
+ u64 size)
{
struct vkms_gem_object *obj;
int ret;
@@ -111,7 +111,6 @@ struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
return ERR_CAST(obj);

ret = drm_gem_handle_create(file, &obj->gem, handle);
- drm_gem_object_put_unlocked(&obj->gem);
if (ret)
return ERR_PTR(ret);

@@ -140,6 +139,8 @@ int vkms_dumb_create(struct drm_file *file, struct drm_device *dev,
args->size = gem_obj->size;
args->pitch = pitch;

+ drm_gem_object_put_unlocked(gem_obj);
+
DRM_DEBUG_DRIVER("Created object of size %lld\n", size);

return 0;
--
2.25.1