On 26/8/21 5:53 pm, Daniel Vetter wrote:
On Thu, Aug 26, 2021 at 10:01:16AM +0800, Desmond Cheong Zhi Xi wrote:
drm_master_release can be called on a drm_file without a master, which
results in a null ptr dereference of file_priv->master->magic_map. The
three cases are:
1. Error path in drm_open_helper
drm_open():
drm_open_helper():
drm_master_open():
drm_new_set_master(); <--- returns -ENOMEM,
drm_file.master not set
drm_file_free():
drm_master_release(); <--- NULL ptr dereference
(file_priv->master->magic_map)
2. Error path in mock_drm_getfile
mock_drm_getfile():
anon_inode_getfile(); <--- returns error, drm_file.master not set
drm_file_free():
drm_master_release(); <--- NULL ptr dereference
(file_priv->master->magic_map)
3. In drm_client_close, as drm_client_open doesn't set up a master
drm_file.master is set up in drm_open_helper through the call to
drm_master_open, so we mirror it with a call to drm_master_release in
drm_close_helper, and remove drm_master_release from drm_file_free to
avoid the null ptr dereference.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
I guess we should also have a cc: stable on this one? I think this bug
existed since pretty much forever, but maybe more prominent with the
drm_client stuff added a while ago.
-Daniel
Thanks for the reviews, Daniel.
Took a closer look. I think if we cc: stable, this fix should accompany
commit 7eeaeb90a6a5 ("drm/file: Don't set master on in-kernel clients")
which moves the drm_master_open out from drm_file_alloc into
drm_open_helper.
---
drivers/gpu/drm/drm_file.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index ed25168619fc..90b62f360da1 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -282,9 +282,6 @@ void drm_file_free(struct drm_file *file)
drm_legacy_ctxbitmap_flush(dev, file);
- if (drm_is_primary_client(file))
- drm_master_release(file);
-
if (dev->driver->postclose)
dev->driver->postclose(dev, file);
@@ -305,6 +302,9 @@ static void drm_close_helper(struct file *filp)
list_del(&file_priv->lhead);
mutex_unlock(&dev->filelist_mutex);
+ if (drm_is_primary_client(file_priv))
+ drm_master_release(file_priv);
+
drm_file_free(file_priv);
}
--
2.25.1
