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authorDesmond Cheong Zhi Xi <desmondcheongzx@gmail.com>2021-07-12 12:35:08 +0800
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-07-20 20:22:19 +0200
commit56f0729a510f92151682ff6c89f69724d5595d6e (patch)
tree79227994f4b4c0df44486cdaa3e6edfec9cc02f8 /include/drm
parent0b0860a3cf5eccf183760b1177a1dcdb821b0b66 (diff)
drm: protect drm_master pointers in drm_lease.c
drm_file->master pointers should be protected by drm_device.master_mutex or drm_file.master_lookup_lock when being dereferenced. However, in drm_lease.c, there are multiple instances where drm_file->master is accessed and dereferenced while neither lock is held. This makes drm_lease.c vulnerable to use-after-free bugs. We address this issue in 2 ways: 1. Add a new drm_file_get_master() function that calls drm_master_get on drm_file->master while holding on to drm_file.master_lookup_lock. Since drm_master_get increments the reference count of master, this prevents master from being freed until we unreference it with drm_master_put. 2. In each case where drm_file->master is directly accessed and eventually dereferenced in drm_lease.c, we wrap the access in a call to the new drm_file_get_master function, then unreference the master pointer once we are done using it. Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-6-desmondcheongzx@gmail.com
Diffstat (limited to 'include/drm')
-rw-r--r--include/drm/drm_auth.h1
-rw-r--r--include/drm/drm_file.h6
2 files changed, 7 insertions, 0 deletions
diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h
index 6bf8b2b78991..f99d3417f304 100644
--- a/include/drm/drm_auth.h
+++ b/include/drm/drm_auth.h
@@ -107,6 +107,7 @@ struct drm_master {
};
struct drm_master *drm_master_get(struct drm_master *master);
+struct drm_master *drm_file_get_master(struct drm_file *file_priv);
void drm_master_put(struct drm_master **master);
bool drm_is_current_master(struct drm_file *fpriv);
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 9b82988e3427..726cfe0ff5f5 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -233,6 +233,12 @@ struct drm_file {
* this only matches &drm_device.master if the master is the currently
* active one.
*
+ * When dereferencing this pointer, either hold struct
+ * &drm_device.master_mutex for the duration of the pointer's use, or
+ * use drm_file_get_master() if struct &drm_device.master_mutex is not
+ * currently held and there is no other need to hold it. This prevents
+ * @master from being freed during use.
+ *
* See also @authentication and @is_master and the :ref:`section on
* primary nodes and authentication <drm_primary_node>`.
*/